Effect of modified dry period lengths and bovine somatotropin on yield and composition of milk from dairy cows.

Dry periods of 40 to 60 d have been an industry standard because dry periods <40 d have resulted in reduced milk yields in the subsequent lactation by 10 to 30%. However, recent research has demonstrated no production losses for cows given a 30-d dry period. The current study evaluated milk production effects of shortened or omitted dry periods for cows at mature-equivalent production >12,000 kg of milk and treated with bovine somatotropin (bST). The study used 2 commercial dairies and one university dairy and included 4 treatments. Five multiparous and 5 primiparous cows from each farm were assigned to each treatment: 1) 60-d dry period, label use of bST (60DD); 2) 30-d dry period, label use of bST (30DD); 3) continuous milking, label use of bST (CMLST); and 4) continuous milking with continuous use of bST (CMCST). Per label, bST use started at 57 to 70 d in milk and ended 14 d before drying (60DD and 30DD) or expected calving date (CMLST). In primiparous cows, average milk yields during the first 17 wk of lactation were reduced for cows on treatments 30DD, CMLST, and CMCST vs. the 60DD treatment. (38.3, 35.1, and 37.5 vs. 44.1 +/- 1.3 kg/d, respectively). For multiparous cows, respective milk yields did not differ (46.6, 43.4, 46.5, and 47.7 +/- 2.1 kg/d). Shortened or omitted dry periods may impede mammary growth in primiparous cows, resulting in reduced milk yield in the subsequent lactation. In contrast, a shortened or omitted dry period with either bST protocol did not alter production in multiparous cows treated with bST. Quality aspects of prepartum milk and colostrum require additional characterization. For multiparous cows, milk income generated for short dry periods or for continuous milking might increase their profitability. At 17 wk of the subsequent lactation, estimates of the cumulative net margins of multiparous cows on the 30DD treatment and continuous milking treatments exceeded those of cows on the 60DD treatment by 40 dollars to 60 dollars per cow.

Dietary fat and ruminally protected amino acids for high producing dairy cows.

Eight early lactation Holstein cows, used in a replicated 4 x 4 Latin square design, were fed the following diets: control; control plus ruminally protected amino acids (15 g methionine and 20 g lysine); control plus added fat (.32 kg 60:40 animal and vegetable blend and .36 kg of Ca salts of fatty acids); control plus ruminally protected amino acids plus added fat. The objective was to examine the effect of ruminally protected forms of lysine and methionine and dietary fat on milk yield and composition. Cows were fed for ad libitum consumption of total mixed diets consisting of 50% forage and 50% concentrate on a DM basis. Added fat increased milk, fat, and 4% FCM yield but decreased milk protein percentage. Ruminally protected amino acids increased milk protein percentage. The combined effect of fat and ruminally protected acids increased milk fat percentage and yield more than the sole addition of either supplement. Added fat increased the percentage and yield of long-chain fatty acids in milk. Plasma free fatty acids were also increased by fat addition. Adding ruminally protected amino acids to fat-supplemented diets may help alleviate the milk protein depression found with added fat.