Effects of a previous treatment with estradiol and progesterone on mammary development and milk production in freemartin heifers artificially induced to lactate

Abstract

Freemartinism is the most frequent type of intersex individual in the bovine species. It is characterized by the birth of a female calf with reproductive developmental anomalies resulting from a twin pregnancy that included a male fetus. Freemartin heifers are usually culled, which causes financial loss to the producer. However, previous studies have shown that freemartin heifers are able to produce milk if properly stimulated by exogenous hormones, although milk production is smaller compared to that of normal lactating cows. Because freemartin heifers do not have ovaries, they are not naturally subjected to the cyclic influence of gonadal steroids. One could speculate that previous exposure to exogenous gonadal steroids in a cyclic pattern, as an attempt to mimic the achievement of puberty and the natural ovarian cycles, could potentially contribute to mammary development and maximize milk production. Therefore, the objective of the present study is to test the hypothesis that a previous treatment with exogenous estradiol and progesterone would increase milk production by freemartin heifers artificially induced to lactate with a standard hormone protocol. Freemartin heifers (n = 8) will be randomly assigned to one of two treatment groups, as follows: heifers receiving a standard lactation-inducing protocol (n = 4) (group LAC); and heifers previously treated with exogenous hormones to mimic ovarian cycles for a period of time (63 days) immediately followed by the standard lactation-inducing protocol (n = 4) (group CiLAC). In the CiLAC treatment group, heifers will receive injectable prostaglandin F2± (PGF2a), estradiol cypionate and benzoate, and an auricular progesterone implant, so that the protocol mimics the occurrence of three estrous cycles. Heifers in both treatment groups will receive the same standard lactation-inducing protocol consisting of bovine somatotropin (bST) on days D0, D7, D14, D21, and every 12 days after D21, when heifers will supposedly be already lactating. From D1 to D7, heifers will receive daily injections of estradiol benzoate and progesterone (i.m.). From D8 to D14, they will receive daily injections of estradiol benzoate only. On D18 and D19, heifers will be treated with PGF2± and from D18 to D20, with dexametasone injections. From D15 to D21, they will be taken to the milk parlor for manual stimulation of the mammary glands. On D22, the first milk collection will take place. Milk production will be monitored throughout seven consecutive months. We hope that this study could contribute to maximizing milk production in freemartin heifers.