The Effects of Dietary Nutrient Concentration, Crumbles Versus Mash and Age of Dam on the Growth of Broiler Chicks

Abstract

Two experiments were conducted to determine the effect of dietary nutrient concentration on the growth response to crumbles compared with mash in broiler starter diets. In the first experiment four diets with similar calorie: protein ratios and calculated energy levels of 2866, 2979, 3090 and 3205 kcal. M.E./kg. were fed ad libitum, as mash and as crumbles, to broiler chicks of mixed sex from 0 to 2 weeks of age. Biological determinations of metabolizable energy were done for the highest and lowest energy diets. These were in good agreement with calculated values. Determined values for crumbles were about one percent higher than corresponding values for mash. Differences between growth increments in favour of crumbles compared with mash were 35, 17, 11 and 9 percent as dietary nutrient concentration increased. With mash, growth rate increased by about 11, 4 and 2 percent for successive increases in dietary nutrient concentration. When the same diets were fed as crumbles no positive response was obtained and the lowest energy diet supported maximum growth. This experiment therefore demonstrated an interaction between dietary nutrient concentration and method of preparing feed.In the second experiment a third variable was introduced, body weight at day-old as influenced by age of dam when hatching eggs were laid, because it was considered that this would affect food intake and might influence the growth response to crumbles. In this experiment the highest and lowest energy diets were fed, as mash and as crumbles, to male chicks from 0 to 4 weeks of age. Half the chicks were obtained from younger dams and average body weight at day-old was 37g. The other half was obtained from older dams and their day-old weight was 44g. There were no significant interactions between dietary nutrient concentration, method of preparing feed and age of dam when hatching eggs were laid, for liveweight gain in the 0 to 4 week period.On average, chicks fed crumbles grew 9 and 6 percent faster than those fed mash, on the lower and higher energy diets respectively. Chicks ate more calories and grew faster on the higher compared with the lower energy diet. In the 0 to 4 week period chicks from older dams ate more food and grew significantly faster than chicks from younger dams. All groups were then fed the same pelleted grower diet from 4 to 8 weeks of age. Differences in early growth rate due to dietary nutrient concentration, crumbles versus mash and age of dam, were no longer apparent by 8 weeks of age.