Effect of rationing grass on the growth rate of dairy heifers and on output per acre, with a note on its significance in experimental design

Abstract

1. A series of three experiments were performed to examine grass as a food for dairy heifers.2. Indoor feeding resulted in lower intakes of herbage and slower growth but gave greater outputs per acre of animal days and live-weight gain than grazing.3. The maximum consumption and growth rate, obtained on young grass, were 2·84 lb. herbage dry matter per 100 lb. live weight per day and 2·2 lb. live-weight gain per day for grazing stock. The corresponding figures for indoor feeding were 2·49 lb. herbage dry matter per 100 lb. per day and 1·34 lb. live weight gain per day.4. Live-weight gain per day was linearly related to herbage dry matter intake from 1·48 to 2·48 lb./ 100 lb. live weight/day.5. Intake of herbage and growth rate only fell after the herbage came into full flower.6. Increased stocking rate had small effects on growth rate because the animals grazed the paddocks more heavily.7. 2·6–3·0 lb. grass dry matter offered per 100 lb. live weight per day was judged an adequate ration for yearling heifers. This gave growth rates of 1·60 lb./day on herbage up to the flowering stage and a consumption of 88% of the available herbage.8. As an experimental technique zero grazing was found inadequate to replace grazing since it fails to reproduce similar intakes and rates of production. It permitted the reduction of intake to sufficiently low levels that live-weight gain per animal and per acre were reduced.9. The greatest output per acre was found to occur between limits of intake per day of 1·8–2·4 lb. herbage dry matter per 100 lb. live weight. Above the point of maximum output per acre level of feeding had little effect on production per animal and rate of stocking controlled output per acre. Below this point level of feeding controlled production per animal. The case is advanced that these latter levels of feeding are necessary in grassland experiments.