Nutritional means of overcoming heat stress in laying hens and broilers.

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.