Maintenance of rations for Merino sheep. II. The performance of weaners fed daily and weekly on rations of wheat and wheaten chaff at maintenance levels and the effect thereon of vitamin A supplements.

Abstract

Groups of Merino weaners were given 3.33 lb starch equivalent (3570 cal of net energy) per sheep per week to maintain body weight a t approximately 40 lb. This nutritional intake was provided by three different rations, namely, 50: 50 and 10: 90 mixtures of wheaten chaff and wheat, and wheat alone. Finely ground limestone was added to each ration to correct the calcium deficiency. One-half of the weaners was drenched early in the experiment . with 500,000 i.u. of vitamin A per head. Each ration was fed to two groups of sheep, one group being fed once a week and the other daily. The weekly fed groups on the high grain rations were brought on to this regime gradually and were then maintained on their rations for 243 days. The surviving sheep in the daily fed groups maintained their mean body weight and general condition as well as did those in the weekly fed groups, but at the end of the experiment the variability in the body weight of the daily fed groups was greater. This was attributed to differences in the rate of food consumption by individual sheep. The death rate in the daily fed groups was 39.8 per cent., compared with 35.4 per cent. in the weekly fed groups. Comparative data are included for similar groups of weaners which were fed ad lib. on 50: 50 and 10: 90 mixtures of wheaten chaff and wheat. Initially, the group fed the 10:90 mixture grew faster but final gains for the whole experimental period of 243 days were significantly greater for the group fed the 50:50 mixture. Plasma vitamin A levels of the weaners which were not treated with vitamin A fell to very low levels and the death rate among these was 63.0 per cent., compared with 16.7 per cent. among those which received the vitamin A supplement. Losses associated with vitamin A deficiency were highest in the groups on the all-wheat rations. The only group in which no losses occurred was that fed ad lib. on the 50:50 mixture of wheaten chaff and wheat. Untreated animals in this group showed depressed vitamin A levels but not to the same extent as those fed ad lib. on the 10: 90 mixture or on the restricted rations. Clinical and post-mortem examinations of weaners which died from vitamin A deficiency showed only signs of anorexia and inanition. Supplementation of a 100 per cent. wheat ration with 0.5 per cent. sodium chloride did not affect body weight changes or eventual losses.