Artificial induction of lactation in unmated heifers and in heifers with reproductive abnormalities

Abstract

Six unmated heifers and six heifers with reproductive abnormalities were induced to lactate artificially. Mammary glands were developed with a series of subcutaneous injections of oestrogen plus progesterone over either 30 or 60 days (priming phase) prior to triggering milk secretion with injections of dexamethasone trimethylacetate. All twelve heifers commenced lactation and the composition of their milk was similar to that of heifers lactating after calving, with the exception that the fat content was consistently high for heifers induced to lactate artificially (ca 4.1% and ca 5.3% respectively). Yields of milk and milk fat for heifers primed for 30 and 60 days, respectively, were not significantly different (P > 0.05) over the first five months of lactation. During this period, the mean milk yield of heifers induced to lactate artificially was 55% and 71%, and their mean yield of fat was 69% and 87% of corresponding yields for heifers lactating after normal and advanced calving, respectively. The hormone treatments did not correct reproductive abnormalities in heifers with aberrant reproductive capacity, neither did they impair reproductive capacity in 'normal' heifers. It appears that a suitable treatment for inducing lactation artificially in non-pregnant dairy cows would be to use a priming phase of 30 days followed by a trigger phase of 3 days.