Biological and economic response of laying hens to dietary lysine and energy contents during peak and late production periods.

Thesis (M.Sc.Agric.)-University of Natal, Pietermaritzburg, 2001.

The effect of dietary energy and amino acid contents during the peak of production of laying hens has been well investigated, but little is known about the late production period. In most of the previous studies the focus has been on improving the performance of laying hens with little, if any, consideration of the costs of achieving the maximum performance. The aim of the present study was, (i) to investigate the effect of dietary lysine and energy contents on the performance of laying hens (ii) to find out whether young (30-40 weeks) and old hens (60-70 weeks) perform the same at given dietary lysine and energy contents, and (iii) to determine the differences in income and costs generated by young and old laying hens. It was hypothesised that young laying hens will perform better and yield more income at given dietary lysine and energy contents than old hens. Two experiments were conducted, during peak (30-40 weeks) and late production period (60-70 weeks) with 240 Lohmann Brown laying hens. For the first experiment, four basal diets, which were a combination of two lysine and two energy levels, were supplied by a commercial feed company. These basal diets were blended with one another in different proportions to produce 15 experimental diets, resulting in five lysine and three energy levels. In the second experiment a feed formulating program (WINFEED) was used to formulate four basal diets with lysine and energy levels that were intended to be close to those used in experiment 1. Due to a blending error, diets with three lysine and five energy levels were produced. This error made it impossible to compare the results of the early and late production period, as originally intended. During both experiments, each bird was allocated between 1.4 and 2 kg feed at the start of each week, when feed was weighed. Egg numbers were recorded daily, at the same time each day, and mean egg weight was recorded by weighing eggs on three consecutive days during each week. It was found that the dietary lysine contents used in both experiments were sufficient to support maximum egg production and that resulted in no statistically significant differences (p>0.05) between treatments being observed in egg production traits (rate of lay, egg weight and egg output). A significant effect of dietary energy content was observed on feed intake, which confirmed that dietary energy content had a significant but indirect effect on egg production, through its effect on the amount of dietary lysine consumed. Older birds were found to be producing 21 g less egg material per day than younger hens, at a given (comparable) dietary lysine and energy content. This result confirmed that older hens require more nutrients to produce a given quantity of egg material. Since the performance of old hens was lower at a given dietary lysine and energy content, the profit generated was also lower. Younger hens generated numerically higher returns than the predicted returns for older hens, at any given combination of dietary lysine and energy tested. However, it was not possible to verify the results statistically, because the expected responses used for older hens were predicted from the results of young hens. In both ages (over the range of dietary lysine and energy contents used) highest returns were realised with the combination of lowest dietary energy and all lysine contents. The effect of a change in egg price was felt more with hens producing heavier egg at both ages, with young hens being more affected than the old hens. The results from these experiments give some indication on trends of returns for hens of both ages, although the economic optimum combinations of dietary energy and lysine could not be predicted (because of the dietary lysine and energy contents used, that were all sufficient to support maximum egg production).