Abstract
We investigated the effects of environmental factors on average daily milk yield and day-to-day variation in milk yield of barn-housed Scottish dairy cows milked with an automated milking system. An incomplete Wood gamma function was fitted to derive parameters describing the milk yield curve including initial milk yield, inclining slope, declining slope, peak milk yield, time of peak, persistency (time in which the cow maintains high yield beyond the peak), and predicted total lactation milk yield (PTLMY). Lactation curves were fitted using generalized linear mixed models incorporating the above parameters (initial milk yield, inclining and declining slopes) and both the indoor and outdoor weather variables (temperature, humidity, and temperature-humidity index) as fixed effects. There was a higher initial milk yield and PTLMY in multiparous cows, but the incline slope parameter and persistency were greatest in primiparous cows. Primiparous cows took 54 d longer to attain a peak yield (mean ± standard error) of 34.25 ± 0.58 kg than multiparous (47.3 ± 0.45 kg); however, multiparous cows yielded 2,209 kg more PTLMY. The best models incorporated 2-d lagged minimum temperature. However, effect of temperature was minimal (primiparous decreased milk yield by 0.006 kg/d and multiparous by 0.001 kg/d for each degree increase in temperature). Both primiparous and multiparous cows significantly decreased in day-to-day variation in milk yield as temperature increased (primiparous cows decreased 0.05 kg/d for every degree increase in 2-d lagged minimum temperature indoors, which was greater than the effect in multiparous cows of 0.008 kg/d). Though the model estimates for both indoor and outdoor were different, a similar pattern of the average daily milk yield and day-to-day variation in milk yield and milk yield's dependence on environmental factors was observed for both primiparous and multiparous cows. In Scotland, primiparous cows were more greatly affected by the 2-d lagged minimum temperature compared with multiparous cows. After peak lactation had been reached, primiparous and multiparous cows decreased milk yield as indoor and outdoor minimum temperature increased.
Highlights
Dairy business success depends on milk yield and quality
Effect of temperature was minimal. Both primiparous and multiparous cows significantly decreased in dayto-day variation in milk yield as temperature increased
Our results indicated that the main effect of the incline slope, decline slope parameters, and −2d.minTb on the log daily milk yield were significant depending on the parity group
Summary
Dairy business success depends on milk yield and quality. Milk yield and the duration of the lactation of a dairy cow is influenced by its genetic capacity, and environmental factors. Though dairy cattle are able to cope with a wide range of climatic conditions, sustainability in the performance of these animals is potentially challenged by climate change, especially as there has been selection for larger breeds such as Holstein (Bos taurus). Meteorological conditions such as ambient temperature, radiant energy, photoperiod, relative humidity (RH), and wind speed contribute to the degree of heat stress events that occurs for the cow (Hammami et al, 2013). At high temperatures and humid climates, animals encounter challenges to Marumo et al.: ENVIRONMENTAL FACTORS ON PRODUCTION IN DAIRY COWS balance the metabolic heat production and dissipate enough heat to their surroundings
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