Nutritional means of overcoming heat stress in laying hens and broilers.
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Date
2003
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Abstract
The relationship existing between the broiler and the laying hen, the methods applied for
estimating the effective energy using linear coefficients to five measurable components of
interactions and their diet used in adjusting ME for heat increment of feeding, the
environment in which they live, the physiological, metabolic, behavioural, and the productive
changes that occur when birds are exposed to heat stress, were studied. Nutrition and
temperature were of particular interest. Each different aspect studied was found to have an
influence on the final performance of the broiler and the laying hen.
Two major experiments were conducted. The objective of the first experiment was to determine
if performance can be improved during hot weather by reducing the heat increment of the
feed. Two EE: ME ratios were used, the low ratio being based on the least - cost feed and the
high ratio being the maximum possible with the available raw materials, and three ND's were
used to determine whether there was an interaction between the ME content of the diet and
the EE:ME ratio. 360, 46-week old Hy-Line Brown layers were housed for ten weeks and
each of these 2 x 3 feeds was replicated four times using 15 hens per replication (three cages
of five hens per cage), making a random allocation of 60 birds per feeding treatment.
Treatment means were calculated for the last seven weeks of the trial. Egg prices (c/egg),
income generated and profit, under normal, 15% increase and 15% decrease for all egg grades
were calculated. It was found that neither the EE nor the ME contents of the feeds had
significant effects on ROL, EW, EO, ADG, or ME intake, though there were some variations
in the response of these variables. Both the EE and the ME of the diet had strong significant
effect (EE at P<O.O 1, ME at P<O.OO 1) on FI, but their interaction had no significant influence
on either the EE intake or FI. The EE intake was highly influenced by both the EE (P<O.OOI)
and ME (P<O.Ol) content of the diet. The amount of feed and energy consumed was primarily
dependent on the dietary energy content of the particular feed, being low at low EE: ME ratio
and high at high EE:ME ratio, respectively, for FI; while energy intake increased positively
with increasing ME content ofthe diet. While ADG increased positively at high EE: ME ratio,
it increased and then decreased at low EE:ME ratio. Feeding cost for the combinations of
dietary EE and ME was found to be linearly increasing and more expensive in treatments with
low EE than in treatments with high EE. Under all circumstances income was positively
related to dietary EE and ME. The highest profit was obtained from diets having high EE: ME
ratios under all egg prices.
The objective of the second trial was to determine the extent to which broilers are able to lose
heat to the environment when forced with conditions that would require them to lose more
heat to the environment than would be possible for them to grow at their potential. The
responses in three lysine-limiting trials were measured at three temperatures, with six diets
and two sexes, and over two growth periods. The first two trials, one being a pilot trial, were
conducted on broilers between 1 and 3 weeks of age, and the third trial was a finisher trial and
was conducted using broilers from 3 to 5 weeks.
Dietary lysine, sex and temperature were found to have a significant effect on ADG (lysine at
P<O.OO 1, sex and temperature at P<0.05) in trial 1, and on FI (lysine and temperature at
P<O.OOI, sex at P<0.05) and ADG (lysine and temperature at P< 0.001, sex at P<O.OI) in trial
2. While dietary lysine, temperature and lysine vs. temperature had significant effect on FCE
in trial 1 (lysine at P<O.OO 1, temperature and lysine vs. temperature at 0.01), only dietary
lysine and temperature had significant effect on FCE (P<O.OO 1) in the pilot trial and trial 2.
While ADG in the pilot trial was significantly affected by dietary lysine and temperature
(lysine at P<O.OO 1, temperature at P<0.05), FI in the pilot trial and trial 2 were significantly
influenced by dietary lysine only (P<O.OO 1). While no interaction had significant effect on FI,
or ADG in both trials 1 and 2, neither sex nor any of the interactions had significant effect on
FCE, FI, or ADG in the pilot trial. In all trials responses in FCE, ADG, and FI showed an
increasing trend with the addition of synthetic lysine (treatment 6 vs. 5), irrespective of
temperature, confirming that lysine was the first limiting nutrient in the summit diets.
Dietary lysine, and temperature were found to have significant effect on protein (dietary
lysine at P<O.OOI, temperature at P = 0.01), lipid (dietary lysine and temperature at P<O.OOI)
and gross energy gain (dietary lysine at P<O.OOI and temperature at P<O.OI) in trial 1, and on
protein gain (P<O.OOI) and lipid gain (dietary lysine at P<O.OOI and temperature at P<O.OI) in
trial 2. All the main effects had significant effect on lipid and gross energy gain (lysine at
P<O.OOI, temperature at P<O.OI and sex at P<O.05) in the pilot trial, and on gross energy
(lysine and temperature at P<O.OOI, and sex at P<O.OI) in trial 2. While the interaction
between temperature and dietary lysine, and temperature and sex had significant effect on
lipid and gross energy gain (P<0.05) in the pilot trial, the interaction between sex and
temperature was found to have a significant effect on protein and gross energy gain (P<0.05)
in trial 1, the interactions between diet and temperature had a significant effect on protein and
gross energy gain (P<0.05) in trial 2. No other interaction had any effect on lipid, gross
energy, or protein gain in any of the trials.
While all the main effects had a significant effect on HL in trial 1 (lysine at P<O.OO 1,
temperature at P<O.OI, and sex at P<O.05), and when the data were combined (lysine and
temperature at P<O.OOI, and sex at P<O.Ol), in trial 2 all the main effects and lysine x sex
(lysine, temperature, and sex vs. lysine at P < 0.001, sex at P < 0.05), in the pilot trial only
temperature and dietary lysine had significant effect (temperature at P <0.001, lysine at
P<0.05)
The constant term and FI were found to have positive relationship with HL, while feather
weight, degree of maturity and temperature were found to have a negative relationship with
HL in both the pilot trial and trial 1. In trial 2, HL showed a positive relationship with FI and
degree of maturity, and a negative relationship with feather weight and temperature. When the
data were combined, HL showed a positive relationship with FI and the constant term and a
negative relationship with feather weight, temperature and degree of maturity. While FI,
temperature, degree of maturity and feather weight were found to have a significant
relationship with HL (P<O.OO 1) in the pilot trial and trial 1, as well as in the combined data, in
trial 2, feather weight and feed intake had a significant relationship with HL.
Description
Thesis (M.Sc.Agric.)-University of Natal, Pietermaritzburg, 2003.
Keywords
Broilers (Chickens)--Feeding and feeds., Broilers (Chickens)--Nutrition., Poultry--Feeding and feeds., Temperature--Physiological effect., Lysine in animal nutrition., Theses--Animal and poultry science.