Author:
Aharoni Y.,Brosh A.,Ezra E.
Abstract
Abstract
Effects of heat load and of photoperiod on lactation performance were
evaluated using milk test data of three Israeli Holstein herds over a period of 3
years, from 1994 to 1996. All together 2209 cows, with 28029 milk records, were
included. Photoperiod effects were examined as associated with day length and
daily changes in day length and heat load index was formulated as a function of
the seasonal day and night ambient temperatures, to account for the heat load
effect. The regression model included effects of cow, herd, year, lactation number
and days in milk in addition to the seasonal effects. The dependent variables were
milk yield and fat, protein and lactose concentrations. Milk yield was affected by
both photoperiod and heat load, with the peak photoperiod effect in May and
amplitude of 3·1 (s.d. 0·9) kg/day and negative heat load effect of-1-8 (s.d. 0·4)
kg/day at its peak. Protein concentration was affected by photoperiod, with the
peak effect in January (amplitude of 1·7 (s.e. 0·5) g/kg) but not by heat load
(-0-2 (s.d. 0·6) glkg). Fat concentration was affected primarily by heat load
(-3-4 (s.d. 0·7) g/kg), with a photoperiod effect which peaked in October
(amplitude of 1·8 (s.d. 0·8) g/kg). Lactose concentration was affected by both
environmental factors to a lesser extent (photoperiod amplitude of 0·6 (s.d. 0·2)
g/kg and heat load effect of-0-03 (s.d. 0·16) g/kg). Comparison of the predicted
seasonal effects on milk yield and composition with the annual fluctuation in the
national herd showed a good match of the predicted effects with the national
observations. It is concluded that while heat load relief may be beneficial,
manipulation of the photoperiod may induce adverse effects on milk yield and
composition.
Publisher
Cambridge University Press (CUP)
Subject
Animal Science and Zoology
Cited by
26 articles.
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