Animal and Poultry Science

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Nutritional restriction of the growth rate of broiler breeder replacement pullets.
(1971) Gous, Robert Mervyn.; Stielau, Werner Johannes.
No abstract available.
The influence of variations in the level of nutrition on reproduction in the ewe.
(1972) Lishman, Arthur William.; Stielau, Werner Johannes.
No abstract available.
The effect of diluent on the bacterial reaction to disinfectants.
(1973) Hathorn, Fergus Ask Shuldham.; Abbott, C. W.
No abstract available.
Estimation of carcass composition of beef cattle by the urea dilution technique.
(1977) Kock, Schalk Willem.; Stielau, Werner Johannes.
No abstract available.
The importance of age at first calving, relationship between body mass and fertility and feeding systems on production in the beef female.
(1978) Meaker, Helgaard Johannes.; Lishman, Arthur William.
No abstract available.
Aspects of the copper-molybdenum-sulphur interactions in sheep.
(1979) Van Ryssen, Jannes Bernardus Jansen.; Stielau, Werner Johannes.
No abstract available.
Biological and economic response of laying hens to dietary isoleucine, methionine, lysine and energy.
(1980) Griessel, Munro.; Gous, Robert Mervyn.
No abstract available.
Response of broiler chickens to dietary lysine, methionine and metabolisable energy concentrations.
(1981) Maclachlan, Rais Guthrie.; Stielau, Werner Johannes.; Gous, Robert Mervyn.
No abstract available.
Luteal function during early post partum in the ewe.
(1984) Grobbelaar, Johan.; Lishman, Arthur William.
No abstract available.
Intensive beef production on cultivated pastures in a sub-tropical environment.
(1984) Louw, Brian Peringuey.; Lishman, Arthur William.
The comparative performance of spring-calving beef cowherds comprising either Dual Purpose (Simmentaler) or British-cross (Hereford x Africaner) cows and calves was investigated at stocking rates of 3,0, 4,12, 5,34 and 6,74 cows and calves/ha on Kikuyu pasture over three seasons. An increase in stocking rate was associated with a decrease in the length of the grazing period, an increase in the mass and condition loss of cows, a decrease in calf livemass gains, a decrease in milk production, an increase in the production of beef per hectare and a decrease in margins over feed costs per cow. Stocking rate did not influence reconception rates, which averaged 65% over the three seasons. Simmentaler cows produced calves approximately 2 kg heavier at birth and 24 kg heavier at weaning, approximately 1,4 litres of milk more per day, lost more condition and attained higher margins over feed costs per cow and per hectare than Hereford-cross cows. Season influenced the length of the grazing season, birth mass, livemass gains in calves and mass changes in cows. Milk production accounted for 40% of the variation in calf gains on pasture. The conversion of milk to calf gain was influenced by milk yield, stocking rate, breed and calf sex. Ovarian and endocrinological responses associated with normal and restricted suckling for a 15-day period at two postpartum stages (Days 35 to 50 and 60 to 75) were examined in Bos taurus and Bos indicus cows. All cows received progestagen therapy, followed by GnRh administration during the periods of variable suckling intensity. Restricted suckling exerted little influence in Bos taurus cows, but tended to improve the ovulatory response, to decrease the incidence of "short" cycles and to increase reconception rates in Bos indicus cows. Treatment exerted no influence on calf growth and on tonic LH and oestrogen secretion. Bos indicus cows suckled normally released more LH in response to GnRh than Bos taurus cows. Bos indicus cows suckled once daily secreted less LH in response to GnRh than those suckled normally. Seasonal effects on tonic LH, and progesterone secretion were studied in cycling Friesland cows. Mean tonic LH levels during autumn were significantly higher than those during summer and spring. Season. exerted no influence on progesterone secretion.
The influence of suckling during early lactation on the resumption of ovarian activity and oestrous behaviour in the Afrikaner cow.
(1986) Wells, Peter Lee.; Lishman, Arthur William.
No abstract available.
The effect of stocking rate on the performance of beef cows and their progeny in the highland sourveld areas of Natal.
(1988) Van Niekerk, Alvin.; Lishman, Arthur William.
In three separate. but related studies, the performance of weaner/replacement heifers, dry pregnant cows, and first calvers and mature cows and their progeny, at different stocking rates in the Highland Sourveld, was investigated. The study area was located in Bioclimatic region 4e in the Province of Natal, Republic of South Africa. In the first study, carried out over four seasons, the effect of winter and summer nutritional levels on the performance of replacement heifers, bred at two years of age, was investigated. The results of this study indicated that compensatory growth was a potentially important factor in reducing feed costs, but the degree of compensation was highly dependent upon stocking rate and the condition of the veld. The most economical regime for rearing heifers up to the mating stage was a low growth rate (0 - 0,25 kg/day) during the first winter (post weaning) followed by a low stocking rate (0,75 AU/ha) on summer veld. Treatment did not generally affect the number of heifers attaining puberty, nor their conception rates. Pregnancy rates as high as 96% were achieved. Treatment also had no apparent effect on subsequent calving rates. In the second series of experiments, the role of condition scoring as a management tool in the Highland Sourveld was studied. The condition score of the cow was shown to be an important factor determining conception rate and time of conception. Only 8% of the cows mated at a condition score of 1,5, conceived, whereas 80% conception rates were achieved when the cows were mated at a condition score of 3,0 - 3,5. The cost of improving a cow's condition from 1,5 to 3,0 was R108, whereas the cost of improving a cow's condition from 2,0 to 3,0 was R54. In the third study, carried out over nine consecutive seasons, the effect of stocking rate and lick supplementation on the performance of iactating cows and first calvers was investigated. Four stocking rates were applied - 0,83, 1,0, 1,25 and 1,67 cows plus calves per hectare. The very high stocking rate was terminated after four seasons because of a significant decline in both cow and calf performance, and the severe deterioration of the natural pasture. There was no benefit to either the cows or calves with access to a urea-based lick at the very high stocking rate, but at the low stocking rate (1,0 cow + calf/ha) the cows were in such a condition that the grazing season could have been extended, thereby saving on winter feed costs. First calvers produced weaners as heavy as those of the mature cows and were in similar body condition at the end of the grazing season. The excellent performance of the first calvers was attributed largely to the fact that they calved 3 - 4 weeks prior to the mature cows. The grazing behaviour of the first calvers and the mature cows, at the different stocking rates, was observed in the fourth study which was carried out over two consecutive seasons. There were no significant differences in the grazing time between the first calvers and the mature cows at any of the stocking rates. In all the treatments, the first calvers appeared to establish the grazing patterns, with the mature cows adopting a followership role. Alloparental behaviour was noted in the early part of both grazing seasons.
Testing the libido of breeding sires to predict mating performance in the field and the hormonal control of male sexual behaviour.
(1988) Crichton, James Spencer.; Lishman, Arthur William.
The incidence of sexually low-response rams was determined in a group of 31 young Ile de France stud rams by means of three libido tests. Eight rams ( 25,8%) we reclassified as being sexually low-response. The proportion of rams showing normal sexual behaviour did not increase over the three tests. As testing progressed the incidence of mounting behaviour increased significantly. The increase in serving activity was non-significant. Following flock mating two low-response rams had not marked any ewes and showed preference for homosexual company. Five of the eight low response rams had a common sire and it is suggested that sexual behaviour may be influenced genetically. A group of 20 month-old beef bulls (n=54) representing nine breeds were evaluated for libido using five serving capacity (SC) tests (bulls tested in groups) followed by one libido score test (bulls tested as individuals). Bos indicus bulls displayed significantly lower SC than bulls from exotic breeds. Bulls underwent a definite learning process over the five SC tests. The increase in SC was not significant for all breeds. The use of oestrous teaser females held no advantage over the use of properly restrained non-oestrous females. Agonistic behaviour did not depress SC (individual exceptions were noted). Growth rate did not have a consistent effect on SC. Activity on the libido score test was highly significantly correlated to SC. The influence of night or day and the presence or absence of an observer on the SC of 20 month-old Bos indicus bulls (n=18) was evaluated over 12 SC tests. Bulls showed no preference for nocturnal sexual behaviour and were not hindered by personnel scoring SC. The improvement in SC with progression of the tests suggested some form of adaption to pen test conditions and/or learning experience. Serving behaviour was however inconsistent from test to test indicating that restrained females do not represent the ideal stimulus. Agonistic interaction depressed SC. Subsequent pasture mating behaviour was significantly related to SC. Some of the factors influencing pasture behaviour are discussed. High SC bulls achieved a conception rate that was 10,8% higher than that of the low SC bulls (difference non-significant). The relationship between bull libido (libido score test) and conception rate following a 21 day breeding season was investigated over two seasons. The average bulling percentages were 2,9 and 2,5% in the first and second seasons respectively. High libido bulls had no advantage over medium libido bulls in both seasons. Bulls achieved acceptable conception rates (> 70%) in both years and it is suggested that the commonly recommended bulling percentage of 4% is conservative. In an investigation into the hormonal control of sexual behaviour in the ram the technique of active immunization against specific steroid hormones was used in an attempt to highlight the possible central action of dihydrotestosterone (DHT) on mounting behaviour. The central aromatization of testosterone gives rise to DHT and oestradiol (E2). Immunization against E2 and a combination of oestrone (E1) and E2 in testosterone propionate (TP) implanted wethers reduced mounting behaviour to animals (no exogenous hormone). levels seen in control Results suggest that DHT has no or limited central nervous action. The effect of DHT appears to be largely via its sensitization of the penis which enhances mounting behaviour in DHT+E2 implanted wethers to levels higher than those recorded in E2 implanted wethers but similar to the activity recorded for wethers receiving TP implants.
Suckling behaviour and fertility in beef cows on pasture.
(1990) Stewart, Iona Boles.; Lishman, Arthur William.
The suckling behaviour of 66 Hereford and Simmentaler cows was studied. The average frequency of suckling in 24 hours was four times, and the average duration of each suckling bout was 10 minutes. Suckling events were not evenly distributed throughout the 24 hour period. Regardless of suckling frequency or days post partum, the most favoured suckling period was between 04:00 and 06:00, i.e. dawn. The lowest incidence of suckling was recorded in the period from midnight to dawn. The longest interval between two suckling bouts over the 24 hours always occurred before the dawn and became longer as the calf grew older (p<0,01). Once the mating season commenced, the onset of oestrus was positively correlated (p<0,01) to the length of the longest inter-suckling period. Suckling behaviour was not affected by the milk yields of the cows studied . In a follow up investigation, 88 cows were separated from their calves for 12 hours out of 24, for the fortnight prior to the start of the breeding season. Fifty-six percent of the 44 cows which were separated from their calves from 18:00 to 06:00 (dayfeeders) exhibited oestrus within 28 days of the breeding season, compared to 22% of the group separated from 06:00 to 18:00 (p<0,01). It was concluded that not only the suppression of suckling may be involved in the onset of ovarian activity . The specific time period during the 24 hours when suckling is prohibited may also play a role.
The effect of form of nitrogen on the efficiency of protein synthesis by rumen bacteria in continuous culture.
(1991) Kernick, Brian Louis.; Van Ryssen, Jannes Bernardus Jansen.; Mackie, Roderick Ian.
The aim of this study was to examine the effect of the form of nitrogen available to mixed rumen bacteria on the efficiency of microbial protein synthesis. A novel, solid substrate, continuous culture fermentor which proved capable of maintaining representative populations of mixed rumen bacteria under steady state conditions, at predetermined growth rates was developed for the study. A series of experiments wherein maize straw, alkaline hydrogen peroxide-treated wheat straw, rye grass or a mixture of maize straw and maize starch were used as substrates were performed in the fermentor. The effect of supplementing these substrates with different forms of nitrogen, namely peptides in the form of a partial hydrolysate of casein, or ammonium salts alone or ammonium salts plus branched-chain volatile fatty acids, on digestion of the substrate and microbial protein synthesis was investigated. Supplementation of maize straw with peptides increased microbial protein synthesis, however this was only significant (P<0.05) when the availability of nitrogen and specific growth rate of the bacteria were not limiting. Organic Matter digestion was not affected by peptide supplementation. Replacement of casein hydrolysate with sunflower oilcake as a source of amino acid nitrogen further increased microbial protein synthesis. The form of nitrogen supplementation did not affect the digestion of constituent cell wall monosaccharides of maize straw. Supplementation of alkaline hydrogen peroxide-treated wheat straw with either branched-chain volatile fatty acids or casein hydrolysate increased the synthesis of microbial protein significantly (P<0.05) and caused a slight, but insignificant increase in the digestion of cellulose-glucose. The efficiency of microbial protein synthesis on rye grass was high, relative to the other substrates, and unaffected by the supplementation of either branched-chain volatile fatty acids or peptides. On media containing high levels of starch, microbial protein synthesis as well as Organic Matter digestion were increased by peptide supplementation, but these differences were only significant (P<0.05) when the bacteria were growing at a high specific growth rate. In all of these experiments, peptide supplementation was accompanied by extensive degradation and deamination of amino acids which offset any increase in microbial protein synthesis. Peptide supplementation therefore resulted in far less efficient overall utilization of protein.
Theoretical and applied aspects of voluntary feed intake by ruminants, with special reference to the kinetics of rumen digestion.
(1994) Pienaar, Johannes Petrus.; Van Ryssen, Jannes Bernardus Jansen.
The aim of these studies was to examine the factors which determine voluntary feed intake and feed quality in ruminants. In the first experiments, the concepts of ruminal digestion kinetics were conceptualised and measured in animals. These concepts were applied practically in feed evaluation studies which followed. In vivo studies on alkali treated wheat straw explained why voluntary intake of ruminants increased when roughages are treated with alkali. The effect of washing the treated feed to remove excess sodium was also studied. The explanation was found in terms of ruminal digestion kinetics, showing that the mean rate of digestion was not changed, but chemical treatment improved the potential digestibility, thereby increasing the active pool size in the rumen which resulted in a faster clearance rate from the rumen. A study of the effect of starch fermentation on the kinetics of roughage fermentation in the rumen, revealed that the fermentation of different diets were affected in a different manner. The paramount factor was found to be a reduced rate of forage fermentation in the presence of starch fermentation in the rumen. A study of Pennisetum clandestinum revealed the reasons why animal performance on kikuyu pasture is often lower than what would be expected from the digestibility and chemical composition of the material. It was shown that a high soluble nitrogen content of the material was the most likely reason for low voluntary intakes, low ruminal fill and therefore poor animal performance on lush kikuyu pasture. A method was developed by which the concepts of ruminal digestion kinetics (MRT method) are used to determine voluntary feed intake with grazing animals. The method gave a mean intake that was similar to the mean obtained when intake was calculated from faecal collections, but had the advantage of a clearer pattern of intake. The accuracy obtained when using the MRT method to estimate voluntary feed intake was confirmed in a second experiment where actual intakes were known, and predicted intake was very close to actual intake. Indirect methods were developed by which two important determinants of voluntary intakes, i.e. rate and extent of digestion may be estimated. The Tilley & Terry in vitro method was adapted to allow the estimation of fermentation rates from rates of gas production. Digestion rates obtained with in vitro gas production agreed well with in sacco estimates. In vivo digestion rates were much slower than those obtained in vitro or in sacco. This discrepancy is yet unexplained, and is in contrast with the results of a previous experiment where in sacco and in vivo results were in good agreement. Increasing the mean particle size of the fennenting forages resulted in a small but statistically significant decrease in fennentation rate. Stirring the fennentation vessels did not have any positive effect on fennentation rate. Total volume of gas produced was not a good indicator of in vitro digestibility because gas production measures ruminal digestion, while in vitro digestibility includes both a ruminal and an acid pepsin phase. The rate of in vitro gas production, as measured by pressure changes in the fennentation vessels, is a practical method that was easily automated by using a data logger. The automated measurement of rate and ex'tent of digestion allows their inclusion into routine analyses for feed evaluation and the results obtained so far indicate that the system is sufficiently accurate to give useful estimates of voluntary feed intake and animal production.
The use of the N-alkane technique for measuring herbage dry matter intake in horses.
(1995) Stevens, Dominic Myles.; Van Ryssen, Jannes Bernardus Jansen.; Stewart, Peter Greig.
The use of n-alkanes as indigestible markers for the estimation of herbage dry matter intake in grazing ruminants, is reported to have significant advantages over other markers used for this purpose (Dove and Mayes, 1991). The use of n-alkanes to estimate herbage intake in horses has not previously been reported, and was therefore investigated in this study. A preliminary trial, carried out in order to investigate possible practical problems in applying the technique to horses, showed that administration of the external marker (C32) in the form of coated grass pellets was satisfactory. Practical difficulties likely to be encountered in carrying out further indoor feeding/faecal collection trials were highlighted during this trial. Four, mature, thoroughbred geldings were used in an indoor feeding and total faecal collection trial to determine the accuracy of intake estimates made using the C31:C32 and C32:C33 n-alkane pairs. The faecal recovery of C31, C32, C33 and C36 as well as the ability of these n-alkanes to provide estimates of diet digestibility were also investigated. Estimates of intake made using the C32:C33 pairs were not significantly different (P< 0.05) from measured intake when the horses were consuming fresh Lolium perenne or Pennisetum clandestinum, P. clandestinum hay or a mixture of concentrates and hay. Overall, error of intake estimate using this n-alkane pair in the total collection trial was 4.8 ± 7%. The C31 :C32 n-alkane pair gave estimates of intake for individual animals that gave significant differences (P<0.05) from measured values when the horses were consuming P. clandestinum hay and the hay + concentrate diet. However, mean intakes were not significantly different (P>0.05) from measured intakes for the fresh L. perenne or P. clandestinum, or hay diet. Overall error in intake estimate was 8.5 ± 16%. Faecal grab samples taken twice daily gave mean estimated intake values which were not significantly different from measured intakes However, estimates of the intake of certain individual animals were found to be significantly different from measured values, using either of the n-alkane pairs. The overall error in intake estimate was 15.1 ± 14% and 4.0 ± 14% for the C31:C32 and C32:C33 estimates respectively. The faecal recovery of the n-alkanes was significantly lower (P< 0.05) when horses consumed L. perenne than when consuming the P. clandestinum grass, grass hay or a mixture of hay and concentrates. The recovery of the C31 , C32 and C33 n-alkanes were similar to those reported for ruminants (Dove and Mayes, 1991). However, there was no significant increase in n-alkane recovery with increasing chain length, and the recovery of C36 was significantly lower than reported in previous studies with ruminants, suggesting differences in behaviour of n-alkanes in the digestive tracts of ruminants and horses. Single doses of C32 resulted in peak faecal concentrations of C32 being reached between 20 and 32 hours after marker administration, after which the levels of the n-alkane decreased rapidly. Complete C32 excretion appeared to be complete 56-64 hours after final dose administration. Single, daily doses of C32 appeared to be insufficient to produce a steady state of faecal C32 marker excretion in the horse, the extent of which may have been influenced by the diet being consumed, resulting in marked diurnal variation in faecal n-alkane concentrations. The results of this trial showed that reasonable estimates of herbage intake in the horse may be obtained using the C32:C33 n-alkane pair. The C31:C32 n-alkane pair was a less reliable indicator of intake but may still be used to provide intake estimates. However, more frequent administration of external n-alkanes than once daily dosing, may be necessary to improve the accuracy of intake estimates made using faecal grab samples, due to the diurnal variation found in this study. The low faecal recovery of the n-alkanes observed in this study made limited their use as digestibility indicators. However, no comparable data is available to confirm the results of this trial. Further investigation is needed with regard to the difference in behaviour of the n-alkanes in the digestive tracts of ruminants and horses. The frequency of external n-alkane marker administration, and the impact of diurnal variation in faecal marker concentration, needs further investigation if the n-alkane technique is to be used successfully with grazing horses.
Capacitation of Nguni semen for in vitro fertilization of bovine oocytes.
(1995) Durrans, Lesley Jane.; Lishman, Arthur William.
In vitro maturation, fertilization and culture is a technique which is increasingly utilised in the animal science industry for embryo production. However, optimal conditions for in vitro maturation, fertilization and culture have not been clearly defined and much research is being done to improve this situation. If these techniques are to be valuable in the production of large numbers of animals in short periods, they must be efficient and reliable. The first part of this investigation aimed to produce comparable rates of fertilization from each of 5 Nguni bulls tested in an in vitro fertilization trial. It was hypothesised that each bull would respond favourably to one or more of the treatments tested. A complete randomised block design was set up to account for block and day effects. A total of 2422 cumulus-oocyte complexes were matured and fertilized with swim-up separated frozen-thawed Nguni semen incubated for 1 min in Ca-ionophore A23187 (0.1, 0.2 or 0.4 µM) or for 15 min in heparin (0.05, 10 or 25 µg/ml). Controls for parthenogenesis and capacitation or acrosome reaction in the fertilization medium were included. Presumptive zygotes were transferred to CR1aa medium and supplemented with 10% and S% FCS on days 4 and 7 post-insemination, respectively. Bull performance was assessed using four criteria: embryo cleavage, a score based on a cleavage index (Score 1; minimum -1, maximum 6) and one which gave greater weight to morulae and blastocysts (Score 2; minimum -1, maximum 10) and blastocyst production. Day effects were highly significant (P<0.001). Parthenogenetic activation of 31.6% of oocytes occurred. Depending on the bull used, cleavage rates (%±s.e.m.) varied from 29.S±2.2 to 40.6±2.6, Score 1 from 0.30±0.07 to 0.6S±0.07, Score 2 from 0.30±0.07 to 0.72±0.08 and % blastocysts from 0.6±0.6 to 4.8± 1.1. Treatment did not significantly affect performance and there were no bull x treatment interactions. However, bull differences in performance were observed. The IVF system employed was not stable and did not produce repeatable results. It was concluded that treatment concentrations tested may have been too low or, alternatively, that treatment effects were being masked by a factor influencing the IVF system more strongly than the treatments tested. In the second part of this investigation, laboratory tests to determine semen quality were examined. It was hypothesised that semen quality would correlate with performance determined during the in vitro trial and, thus, provide predictors for bull fertility in vitro. A dual staining procedure which detects live/dead or acrosome reacted/not acrosome reacted sperm was also utilised to determine whether bull x treatment interactions may have existed in the in vitro trial but were obscured by other factors influencing the IVF system. Sperm motility and abnormal morphology were assessed using light microscopy on whole frozen-thawed semen samples. Statistical analysis could not be done because of lack of replication. Percentages of immotile sperm were high (60.16% to 78.51%), with considerable variation in progressive motility (13.90% to 34.35%) between bulls. A large variation in numbers of morphologically normal sperm was observed between bulls (66% to 90%), with major deformities (9% to 19%) accounting for most of the abnormalities. High negative correlations with performance (as defined in the in vitro trial) were found between % normal sperm and % proximal droplets (r=-0.66 to -0.88). Percentage of minor abnormalities, distal droplets and coiled tails correlated positively with fertility (r=0.67 to 0.91). Motility did not correlate highly with any of the criteria used to assess bull performance. Correlations of semen quality to performance were contradictory to expected results and this may have been due to swim-up separation of sperm for the in vitro trial which was not carried out for semen quality assessment. At present, these semen quality tests do not allow prediction of bull fertility in vitro. Assessment of sperm stained for evaluation of live/dead and acrosome reacted/not acrosome reacted was a lengthy procedure. Again, statistical analysis was not possible due to the lack of replication. High percentages of sperm were characterised as dead (52.4% to 100%). Bulls did respond differently to the various treatments, as determined by the proportion of acrosome reacted sperm and live acrosome reacted sperm. Thus, bull x treatment interactions were apparent, suggesting that the IVF system was more strongly influenced by other factor(s) which reduced sensitivity to the treatments tested. In summary, more research is needed to stabilise the IVF system if production of large numbers of embryos is to become economically viable.
The effect of different methods of controlling urolithiasis on ovine mineral metabolism.
(1995) MacCallum, Kim Barbra.; Van Ryssen, Jannes Bernardus Jansen.
The widespread use of high-energy, low roughage diets among feedlot sheep has lead to the development of several production diseases (Bide et al., 1973). One of the least easily identifiable is urolithiasis, yet it is an important cause of death among feedlot sheep (Emerick, 1988). The primary causative factors of urolithiasis are an alkaline urine and a high urinary P level (Bushman et al., 1965a, 1965b, 1968). The prevention of this disease therefore involves the use of an anionic salt such as NH4Cl in the diet, to acidify the urine, or the use of a high Ca:P ratio in order to decrease urinary P levels (Bushman et al., 1965a; Robbins et al., 1965). At present NH4Cl is included in sheep rations with the express purpose of preventing urolithiasis. However, this method has a disadvantage as anionic salts have been shown to cause metabolic acidosis (Harmon & Britton, 1983) and therefore the second means of prevention, that of a high Ca:P ratio, may be the more suitable method. For this reason, an experiment was designed in order to determine whether NH4Cl or a high Ca:P ratio was the better method of urolithiasis prevention with respect to the animal's performance, mineral metabolism and acid-base status. Furthermore, the effect of Ca and NH4Cl on Se metabolism was studied as very little work has previously been done on this subject. With this objective in mind, a growth trial and digestibility study were conducted. For the growth trial, a 3 x 2 x 2 factorial experiment was designed with three levels of NH4Cl (0, 0.75 and 1.5%) at a high (4: 1) and medium (2.5: 1) Ca:P ratio. Se was included in the diet at a level of 0 and 0.3mg/kg. The trial extended over a period of 74 days, and during this time weight and feed intake were measured, and blood, urine and faecal samples were collected for mineral and acid-base status analysis. At slaughter, the liver, kidney, heart, pancreas and a portion of the Longissimus dorsi muscle were removed for mineral analysis. Fluid from various sections of the digestive tract was sampled for digesta pH determination. The digestibility trial was designed as a 4 x 4 latin square change-over design which was based upon a ten day preliminary period and a five day collection period. Urine volume and pH were measured, and faecal mass and feed intake recorded to allow for the determination of the digestibility of the treatment feeds. NH4Cl was found to affect most criteria considered. Increasing levels of NH4Cl caused performance criteria (mass and feed intake) to decrease, as did blood pH, HC03 and BE values. Liver and kidney dry mass, and the urinary excretion of Ca, P and Mg increased. Urine pH and faecal mineral excretion decreased. The effect of 0.75 % NH4Cl on the animal was not significantly different to that of the 0% NH4Cl diet. However, 1.5% NH4Cl had a significantly adverse effect on the animal. The high Ca: P ratio was found to improve mineral retention although absorption decreased as evidenced by an increased faecal mineral excretion. Blood acid-base status was adversely affected by the higher limestone level as blood pC02 levels increased causing blood pH to decrease. Thus, a high limestone level was symptomatic of respiratory acidosis, although blood pC02 levels were not sufficiently high to allow for this classification. The NH4Cl x Se interaction significantly affected blood acid-base status, urine pH and urinary P excretion. The addition of Se to the diet was found to have a slight alkalizing effect on the animal, as it raised blood acid-base status and urine pH above that of the diet containing no additional Se. The NH4Cl x Se interaction also caused urinary P excretion to increase, especially at an NH4Cl level of 1.5%. The NH4Cl x Ca interaction produced varied results, as the high Ca x 1.5% NH4Cl diet had the most detrimental effect on mass and feed criteria and blood BE values, while the most acidic combination according to abomasal and duodenal pH, blood pH, urine volume and urinary mineral excretion was the medium Ca x 1.5% NH4Cl diet. From the results of the current investigation, it was concluded that the best method of preventing urolithiasis was through the addition of 0.75% NH4Cl to the diet, as this resulted in an acidic urine and yet had no significantly adverse effect on the performance, mineral metabolism or acid-base status of the animal.
Performance of Hereford and Holstein heifers on kikuyu pasture (Pennisetum clandestinum), using n-alkanes for determination of digestibility and dry matter intake.
(1995) Horne, Tim.; Stewart, Peter Greig.
Kikuyu pasture (Pennisetum clandestinum) is potentially the most important source of roughage used to feed dairy heifers in summer in KwaZulu-Natal. It is commonly believed that on kikuyu pasture beef breed females grow at a faster rate than those from dairy breeds when no supplementation is given. Little conclusive evidence is, however, available to support this. Explanations as to why such differences may exist are also limited. Eight Hereford and eight Holstein heifers of similar age and maturity stage were used in a trial. The trial was run over a twenty week period. For the first ten weeks all the animals in the trial grazed ad libitum kikuyu pasture with no supplementation except for a mineral lick. Over this (grass only) period the two breed groups formed the two treatments. During the second ten week period of the trial all of the Holsteins and four of the Herefords were fed a restricted but equivalent amount (1 .7 kg) of a maize meal based concentrate. The use of a computerized, mobile feeding system allowed concentrate intake of individual animals to be measured. Animal height, weight and condition score readings were taken weekly over the grass only and the concentrate (final seven weeks) periods of the trial. Herbage intake and digestibility were estimated using n-alkanes as indigestible markers in two experiments conducted during the grass only and concentrate periods. The Herefords had a significantly higher ADG than the Holsteins (0.82 vs. 0.04 kg/day; P < 0.01) over the grass only period. During the concentrate period the rate of mass gain of the Holstein treatment did not differ significantly (P >0.05) from the Hereford treatment receiving concentrate. The Herefords receiving concentrate were also not significantly different (P > 0.05) in rate of mass gain from the Herefords not receiving concentrate. Rate of height gain was not significantly different (P> 0.05) between treatments over either the concentrate or the grass only periods. During the grass only period the Holsteins lost condition (0.07 condition score units per week) whilst the Herefords gained condition at an equivalent rate. The voluntary intake of concentrates was not significantly different (P > 0.05) between the Herefords and Holsteins (19.19 vs. 16.40 g/kg/L.W(liveweight) (0.75)). Regression coefficients relating level of concentrate intake to rate of mass gain were also not significant (P > 0.05) for either of the treatments receiving concentrate. The use of n-alkanes as indigestible markers showed the intake of the Holstein treatment to have an intake 55% (P < 0.0 1) higher than the Herefords (185.4 vs. 120.5 g/kg L.W(0.75)) over the first experiment where both treatments were grazing ad lib. kikuyu alone (grass only period). During the concentrate period intake of the Herefords receiving concentrate exceeded that of the Holsteins (P < 0.01) by 23% (139.1 vs. 113.1 g/kg L.W(0.75)). Review of the literature, suggests that the double alkanes technique greatly over-estimated intake. Errors in herbage sampling (accentuated by pasture rotation in the first experiment), a low daily dose of the synthetic alkane (C(32)) and incorrect estimation of the C(32) content in the daily doses are identified as possible causes of the over-estimation of intake. Faecal recoveries of the herbage n-alkanes were demonstrated to increase with increasing chain length and hence C(35) was proposed as the most reliable herbage alkane for dry matter digestibility determination. Digestibility differences between treatments estimated using the C(35) alkane were not significantly different (P > 0.05) in either the first or second experiments. The mean digestibility estimates (using the C(35) alkane) for the first and second experiments were 64.9 and 56.61 %, respectively. In conclusion, higher growth rates of Herefords on kikuyu pasture would seem to be primarily due to differences in the dry matter intake of the grazed herbage. Further work using other breeds of dairy and beef animals is required. The underlying cause of differences in dry matter intake between breeds also requires investigation.

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