Artificially extending photoperiod improves milk yield in dairy goats and is most effective in late lactation

Abstract

Short day length (i.e. winter) is associated with reduced milk yield from dairy animals. Dairy cows and sheep have been successfully housed under lights throughout winter to extend the day length and increase milk yield, very little data exists on the effect of extended day length on the milk yield of dairy goats. The current study was conducted over an eight week period from June to August, 2009. A total of 542 Saanan and Saanan British Alpine cross goats were used, all producing ≥1.5L of milk per day, 253 in early lactation (5–20 days in milk) and 289 in late lactation (190–210 days in milk). Does were randomly allocated to either the control or the long day photoperiod (LDPP) groups, both were housed in open sided sheds with the LDPP group exposed to 16h of light, while the other received a natural lighting regime. Milking was conducted by machine and yield was automatically recorded daily. Doe weights were measured at the beginning of the study and subsequently at four-week intervals. Milk and blood samples were collected from a subset (n=30 and n=18 respectively) of animals in each of the four groups, at day 0 and then every four weeks. Milk was analysed for protein, lactose, bulk milk cell count (SCC), fat and solids-not-fat. Blood plasma was assayed for glucose, non-esterified fatty acids (NEFA) and prolactin. Treatment with LDPP significantly increased (P<0.001) milk yield, with the greatest response occurring in late lactation animals, who were producing 20% more milk than their control counterparts (+0.28kg/d). An increase in milk yield was evident by week 1 in late lactation and week 4 in early lactation. Overall, goats exposed to LDPP showed a decrease in milk fat % (P=0.003), milk protein % (P<0.001), milk solids not fat (P<0.001) and somatic cell count (P=0.012), but a slightly higher milk lactose % (P=0.010), when compared to control animals. LDPP increased milk protein (P=0.010), lactose (P=0.032) and SNF yield (P=0.034) in late lactation animals with the response being greater after 8 weeks than after 4 weeks of treatment. Plasma prolactin (P=0.007) and glucose increased with exposure to LDPP while the same animals showed a decrease in plasma NEFA. Liveweight increased (P<0.001) with LDPP exposure, was greater (P<0.001) in late lactation than in early lactation and increased (P<0.001) with week of treatment. Exposure to LDPP significantly increased milk yield and lactation persistence in Australian dairy goats, most substantially in late lactation.