Effect of Modified Dry Period Lengths and Bovine Somatotropin on Yield and Composition of Milk from Dairy Cows

Abstract

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.

Effects of continuous lactation and short dry periods on mammary function and animal health

“…Mammary involution and growth occur during the dry period and the rate of this process is an important factor for milk production efficiency in the next lactation. As previously mentioned, we and others have hypothesized that CM and SDP do not permit sufficient time for involution (loss of secretory function and some presumed loss of epithelial cell number) and cell proliferation/replacement (Capuco and Akers, 1999;Annen et al, 2004a;Pezeshki et al, 2010). The reduced milk yield response to CM is most apparent in primiparous animals and is reduced as number of parities increases (Remond et al, 1992;Annen et al, 2004b).…”

“…However, a 30-day SDP in multiparous cows has often been shown to have no impact on subsequent milk yield. When the additional 30 days of production in the previous lactation are included in the milk yield estimate there is often a production advantage for use of 30-day SDP in multiparous cows (Annen et al, 2004a;Pezeshki et al, 2007 and.…”

“…Although some studies have reported that omitting the dry period did not have an impact on the milk production of the next lactation either without using bovine rbST in dairy cows (Remond and Bonnefoy, 1997) or using bovine somatotropin (bST) in multiparous cows (Annen et al, 2004a), in most studies it has resulted in production losses of 10% to 40% in the subsequent lactation (Andersen et al, 2005;Fitzgerald et al, 2007).…”

“…The changes of milk protein percentage in the subsequent lactation after modifying the length of the dry period have been variable. The protein percentage during the following lactation was reported to be increased (Annen et al, 2004a (primiparous cows); Andersen et al, 2005;Watters et al, 2008) or unaffected (Annen et al, 2004a (multiparous cows) andPezeshki et al, 2008) following SDP or CM. Greater milk protein percentage in cows with shortened or eliminated dry periods may be explained by reduced milk yield in these cows (dilution effect) or improved energy balance, and thereby sparing amino acids and energy for protein synthesis (Remond et al, 1997a).…”

“…Progenitor cells are responsible for expanding and maintaining the number of mammary secretory cells (Capuco and Akers, 1999). Senescent MECs that are carried over into the following lactation may reduce the gland's secretory capability (Capuco and Akers, 1999;Annen et al, 2004a). Thus, the current understanding is that the dry period is required for normal cell turnover and regeneration between lactations.…”