Effects of Long Daily Photoperiod and Bovine Somatotropin (Trobest®) on Milk Yield in Cows

Abstract

Bovine somatotropin (bST) and exposure to long daily photoperiod increase milk yield of dairy cattle. We tested the hypothesis that long daily photoperiod and bST treatment would increase milk yield in an additive manner in lactating cows. At winter solstice, 40 lactating cows were started on a 140-d experiment; cows were greater than 70 d in milk (DIM) and were balanced for uniformity of DIM and milk yield within parity. Cows were randomly assigned to one of four treatments (10/treatment): 1) natural photoperiod, 2) natural photoperiod + bST (14 mg/d Trobest i.m.), 3) long daily photoperiod (18 h of light and 6 h of darkness/d), or 4) long daily photoperiod + bST. Long daily photoperiod increased fat-corrected milk (FCM) yield 1.9 kg/d versus natural photoperiod. Treatment with bST increased FCM 5.7 kg/d versus natural photoperiod, and long daily photoperiod + bST increased FCM 5.8 kg/d versus long daily photoperiod. Long daily photoperiod + bST was additive, increasing FCM 7.7 kg/d versus natural photoperiod. Serum somatotropin increased with bST, but not photoperiod, and bST increased serum insulin-like growth factor-I. Long daily photoperiod tended to increase prolactin; bST had no effect. Long daily photoperiod + bST increased dry matter intake (DMI) relative to natural photoperiod and natural photoperiod + bST; long daily photoperiod increased DMI relative to natural photoperiod + bST. Photoperiod had no effect on net energy balance; however, bST decreased net energy balance. Generally, body weight and milk composition did not differ among treatments. In conclusion, combination of bST with long-daily photoperiod tended to amplify the increases in milk yield observed with either treatment individually.

Regulation of Mammary Development as It Relates to Changes in Milk Production Efficiency

“…Exposure of dairy cows to long day photoperiod (16 h light: 8 h dark) during established lactation was associated with increased milk production (Peters et al, 1981;Evans & Hacker, 1989;Miller et al, 1999). In contrast, exposure to short day photoperiod (8h light: 16h dark) during the last 2 mo of pregnancy was associated with an increase in milk yield in the subsequent lactation (Miller et al, 2000).…”

“…During established lactation, manipulation of photoperiod appears to influence lactation persistency (Peters et al, 1981;Evans & Hacker, 1989;Miller et al, 1999), whereas manipulation of photoperiod during the non-lactating period had no effect on subsequent lactation persistency (Miller et al, 2000). Despite the uncertainty with respect to the underlying mechanisms, and whether there is truly an effect on lactation persistency, manipulation of photoperiod has emerged as an effective management strategy to improve milk production efficiency of dairy cows (Dahl & Petitclerc, 2003).…”

Photoperiod and bromocriptine treatment effects on expression of prolactin receptor mRNA in bovine liver, mammary gland and peripheral blood lymphocytes

“…Within 2 h of collection, plasma for hormone determination was obtained from whole blood after centrifugation (1850 g, 20 min, 4 C) and stored at -20 C until assayed for PRL. Serum PRL concentrations were determined by RIA as described by Miller et al (1999). Mean intraassay coefficients of variation (three assays) for medium (6·5 ng/ ml) and high (11·8 ng/ml) control pools of sera were 3·3 and 9·6% respectively.…”

Enfriamiento al inicio de verano para mitigar el estrés por calor en vacas Holstein del noroeste de México

“…Metabolic regulation of GH and IGF1 allows to prioritize some emerging functions such as the adaptive response to a warm climate in transition for lactation maintenance of milking cattle. The PRL activates milk synthesis in ruminants, however, it is not essential for lactation maintenance (36) , while the IGF1 pathway stimulates galactophoyesis and interacts by separate with PRL and STB (37) . It explains the reduction in PRL levels and the increasing in IGF1 levels during the warmest period of this study.…”

“…La regulación metabólica de PRL e IGF1 permite priorizar algunas funciones emergentes como la del intento de adaptarse a un clima cálido en transición y mantener una lactancia (por demanda ambiental) en ganado especializado, aún en bajos niveles. La PRL tiene acción en la síntesis de leche en rumiantes, sin embargo, no es esencial para mantener la lactancia (36) , mientras que la ruta del IGF1 estimula la galactopoyesis e interactúa en forma independiente de la prolactina y STB (37) . Lo anterior, puede explicar la caída en los niveles de PRL y el incremento del IGF1 en el periodo más cálido de este estudio.…”