The digestibility, intake and faecal marker patterns of Hereford and Friesland bulls consuming kikuyu (Pennisetum clandestinum) using N- alkanes.
Kikuyu is an important summer pasture species in South Africa for animal production, and is seemly suitable for growing out dairy replacement heifers. Previous research by Horne (1996) and Fushai (1997) showed that Friesland heifers had disappointing growth performance on kikuyu and concluded that there was an intake problem. In this study, Friesland (FB) and Hereford bulls (HB) were compared (with respect to growth, intake digestibility, faecal marker excretion patterns and time spent grazing) to investigate the previously identified intake problem of Friesland heifers. Growth parameters (weight, height and condition score) were measured (during summer and autumn) for five FB (remaining three Friesland bulls were excluded due to disease) and eight HB while on kikuyu pasture. The average daily gain was 0.66 kg per day with no significant difference between treatments. Average height and condition score gain were not significantly different. The alkane method was used (and was compared with Calan gate intake estimates) to determine intake and digestibility estimates (seven days). The alkane method compared favourably with the Calan gate estimation of feed intake (coefficient of variation was 22 %). No significant differences were found between the breeds for intake and the average intake was 93 g DM/kg W 0.75/day. Apparent dry matter digestibility (calculated by alkane method) was 6 % higher (P < 0.05) in the Friesland bulls over the Hereford bulls. Apparent dry matter digestibility estimates were measured (three FB and three HB; five days) while animals were confined to metabolic crates. Dry matter digestibility was not significantly different between treatments with the average estimate being 696 g/kg DM. However, intake was 11 % greater (P < 0.05) for the Friesland bulls when expressed on a metabolic basis (g DM/kg W 0.75/day). Amount of faeces produced and nutrient digestibility estimates (crude protein, NDF and ADF) were the same for the breeds. The dry matter of faeces varied in that the Friesland bulls produced faeces 25 % drier than the Hereford bulls. Faecal marker excretion patterns were plotted (four days) after oral administration of an alkane marker (three FB and three HB). The Grovum and Williams (1973) model indicated no significant differences in the digesta flow between treatments. Mean retention time was 45 hours for the alkane marker. QDQ curve analysis fitted two separate curves (r 2 =0.91) but peak times were not significantly different. The average peak time was 23.7 hours. A gompertz curve (r 2 =0.97) was fitted to accumulated marker concentration. Linear parameters were significantly different, the Hereford bulls having a greater accumulation of marker concentration over time. Animal activity (time spent grazing, ruminating and idling) was recorded over a 24 hour period (five FB and eight HB). The study was performed twice. There was no significant difference in animal activity between the breeds. The average bull spent 30 % of the day grazing, 34 % of the day ruminating and 36 % of the day was spent idling. At slaughter the heart, liver, lungs and spleen were weighed (five FB and five HB). No significant differences were found when organ weight was divided by metabolic weight. No significant differences were found in the growth rate, feed intake and feed digestibility when comparing Friesland and Hereford bulls on kikuyu pasture, in contrast to the findings of Horne (1996) and Fushai (1997) using Friesland heifers.