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Photoperiod on Growth and Milk Production in Cattle


Cows walking to the barn.

For a review of this topic see Dahl et al. (2000) in the reference list.

Effects of light on growth in heifers: Giving heifers 16 hr of light daily increased rate of body growth 10-15% during fall and winter months (this work was done in Michigan, where natural lighting was 9-12 hr light/day). This growth occurred without a proportional increase in feed intake. Increased body wt. was due to protein gain, not body fat. This effect did not occur in growing steers. The increased length of day light did increase PRL, but did not increase GH concentrations in the blood. The response also may involve the effect of light on melatonin (see Stanisiewski et al., 1988, J. Anim. Sci. 66:464). [See also: Tucker and Ringer, 1982, Science 216:1381; Petitclerc et al., 1983, J. Anim. Sci. 57:892; Tucker et al., 1984, J. Anim. Sci. 59:1610; Zinn et al., J. Anim. Sci. 62:1273 , 1986; and Zinn et al., 1989, J. Anim. Sci.67:1249.]

Effects of light on mammary growth in heifers: Mammary growth was stimulated by 16 : 8 (hr light : dark cycle) compared to 8 : 16, in prepubertal and postpubertal heifers. [See Petitclerc et al., 1985, J. Dairy Sci. 68:86.]

Effects of light on milk yield: Cows given 16 hr of light daily increased milk yields by about 10% during the fall and winter. Intake was increased sufficiently to account for increased milk yield. [See Peters et al., 1978, Science 199:911; Peters et al., 1981, J. Dairy Sci. 64:1671; Marcek and Swanson, 1984, J. Dairy Sci. 67:2380; and Stanisiewski et al., J. Dairy Sci. 68:1134, 1985.]

Many stimuli can alter blood PRL levels, especially TEMPERATURE and LIGHT:

Generally, as temperature increases, blood PRL concentrations increase, and as day-length increases, blood PRL concentrations increase, although this response lags a few days behind the change in day-length. Blood PRL concentrations also respond to other stimuli such as stress. Great care must be taken when collecting blood samples from animals not to stress the animal.

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