PROTEIN DEGRADABILITY AND CALCIUM SALTS OF LONG-CHAIN FATTY-ACIDS IN THE DIETS OF LACTATING DAIRY-COWS - REPRODUCTIVE RESPONSES

Multiparous Holstein cows (n = 45) were assigned at calving to one of four diets arranged in a 2 x 2 factorial design. The two main factors were dietary concentration (dry matter basis) of 1) degradable intake protein (11.1 or 15.7%) and 2) supplemental fat (Ca salts of long-chai n fatty acids; 0 or 2.2%). Soybean meal and urea were replaced with le ss degradable protein meals (corn gluten meal, meat and bone meal, fis h meal, and blood meal). During the first 9 wk postpartum, cows fed di ets containing the greater concentration of highly degradable protein demonstrated less follicular development on their ovaries, were delaye d in their first luteal activity postpartum (25.2 vs. 38.6 d), accumul ated less luteal tissue (<15 vs. >70 mm), and had lower plasma progest erone accumulated over time. The supplementation of Ca salts of long-c hain fatty acids to the 15.7% degradable protein diet doubled the numb er of corpora lutea, reduced time to first rise in progesterone by 6 d , doubled the number of normal luteal phases, and restored the pattern of accumulated plasma progesterone concentrations to a pattern that w as similar to that induced by other diets. Cows were synchronized to e strus and inseminated at approximately 65 d postpartum. Pregnancy rate was increased from 52.3 to 86.4% when fat was supplemented. Cows fed fat tended to have more corpora lutea and a larger corpus luteum and a ccumulated more plasma progesterone than did cows not fed fat. Diets c ontaining excess degradable protein or Ca salts of long-chain fatty ac ids influenced ovarian structures and reproductive performance.