Effect of Seriously Restricted Growth Upon Lactation

One mate from each of nine pairs of identical-twin dairy heifers was reared on normal feed, including alfalfa-grass hay ad lib. and concentrates up to one year. The other pair-mates were fed only hay, and from 4 to 24 months their consumption was restricted to 66% of the normal TDN. This feed restriction kept the body weights of the underfed heifers about 25% below normal. Breeding difficulty and loss due to difficult parturitions caused removal of three pairs. The six remaining pairs were fed alike after first parturition for comparisons through three lactations. The average daily TDN intake of these six pairs from 4 to 24 months was 7.8lb for the normals and 5.2lb for the subnormals. They weighed 743 and 582lb, respectively, at first parturition. During the first lactation an average of 13.4 and 12.8lb TDN was consumed daily by the normals and subnormals, respectively. Their respective first-lactation yields of FCM were 4,745 and 4,117lb. During the first lactation the subnormal twins increased in body weight from 78 to 95% of the normals. In the second and third lactations the pair-mates produced nearly alike, showing no harmful effect on lactation of subnormal growth after the first lactation. The normal cows remained slightly larger in body size than their restricted-growth mates through to mature size.