Influence of nutrition of mammary development in pre- and postpubertal heifers.

This experiment investigated the influence of plane of nutrition on mammary development in heifers. Prepubertal and postpubertal heifers were fed a ration 60:40 concentrate to forage in restricted or ad libitum amounts. Dry matter intake of the heifers on restricted feeding was 60% that of heifers fed ad libitum. Average daily gain of heifers on restricted feeding was 613 g compared with 1218 g for heifers fed ad libitum. Ad libitum feeding during prepuberty lowered mammary secretory tissue weights 23% and deoxyribonucleic acid content 32% compared to restricted feeding. In contrast, there was no difference in growth of mammary secretory tissue between postpubertal heifers fed restricted or ad libitum amounts. Composition of mammary parenchyma was not affected by plane of nutrition in prepubertal or postpubertal heifers. From these data, we suggest a critical period for total mammary cell number in heifers during which mammary growth is affected adversely by a high plane of nutrition.