Effects of MGA on Prepubertal Crossbred Beef Heifers

A two year study (1995 and 1996) was utilized to study the effects of feeding MGA to prepubertal beef heifers to induce puberty. Heifers were allotted to two groups, control or treatment, based on breed, age and weight. Treatment heifers received MGA for 14 data rate of .4 mg/d with their diet while control heifers received the same diet free of MGA. In year one (n=55; control=28, treatment=27), heifers weighed 285.3 kg and were 301.9 d of age at the start of the treatment. No difference in age at puberty (P=.65) was present with control heifers 378.5±8.3 d of age and treatment heifers 373.0±8.5 d of age. Forty-seven of 55 heifers became pregnant to the breeding season (85.5%). Of the 47 heifers, 37 heifers gave birth to a live calf (78.7%). In year two (n=41; control=20, treatment=21), heifers were 276.8 kg and 300.4 d of age at the start of the treatment. Control heifers were 373.6±7.3 d of age and treatment heifers were 382.4±7.3 d of age at puberty (P=.40). Thirty-eight of 41 heifers became pregnant to the breeding season (92.7%). Thirty-five of 41 heifers were bred AI (85.4%). Thirteen of 16 control heifers and 12 of 19 treatment heifers became pregnant to AI (P\u3e.50). At the CCU (n=24; control= 12, treatment= 12), heifers weighed 318.0 kg and were 309.0 d of age at the start of the treatment. There was no statistically difference in age at puberty (P=.12). Control heifers were 399.5±10.7 d of age and treatment heifers were 375.2±10.7 d of age at puberty. Twenty of 24 heifers became pregnant during the breeding season (83.3%) with 10 heifers from each treatment pregnant. Eight of 11 control heifers and 8 of 12 treatment heifers became pregnant to AI (P\u3e.75). The use of MGA to induce puberty has potential, but further research is needed to determine the age at which it should be administered