Graduate Thesis Or Dissertation

 

The effect of photoperiod on milk production and prolactin in Holstein dairy cows Public Deposited

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  • Fourteen multiparous Holstein cows were paired by stage of lactation and previous years milk yield and 14 Holstein first-calf heifers were paired by stage of lactation. One member of each pair was assigned to a 24L:OD or a 18L:6D photoperiod for 16 wk during winter 1981 (Experiment 1). A similar experiment comparing natural photoperiod (9-12 h light/day) and 18L:6D was conducted for 9 wk during winter 1982 (Experiment 2) in which 24 Holstein cows and 22 Holstein first-calf heifers were paired and assigned to groups as in the first experiment. Animals were housed in a free stall barn open on 2 sides. High pressure sodium vapor lamps provided light intensity at cow eye level of 254 26 lux during the day and 132 9 lux at night. In Experiment 1, concentration of serum prolactin (PRL) in response to thyrotropin releasing hormone (TRH)(33 μg/100 kg BW) was measured in 5 animals from each group. Prolactin response to TRH or saline was tested in 10 animals in each group in Experiment 2. Photoperiod had no effect on 4% fat corrected milk (FCM) in either age group in Experiment 1 although cows in the 18L:6D group averaged 2% higher monthly persistency in 4% FCM over the 12 wk that milk composition was monitered. Cows in the 18L:6D group averaged 5% higher monthly persistency in 4% FCM in Experiment 2 as compared to cows exposed to a natural photoperiod. Persistency in heifers was unaffected by photoperiod in this experiment. Basal concentration of serum PRL was not affected by either age or photoperiod in Experiment 1 (21.3±3.3 ng/ml). Peak concentration of serum PRL after TRH injection was not affected by photoperiod in the heifer group but cows exposed to 18L:6D had significantly higher concentrations of serum PRL after TRH injection than cows exposed to 24L:0D (560±133 vs. 229±54 ng/ml). Basal concentration of serum PRL in Experiment 2 was similar in TRH- and saline-injected animals (26.3±3.1 ng/ml) but was lower in cows than in heifers (17.1±2.0 vs. 35.5±5.0 ng/ml). Saline injection did not elicit a PRL increase nor were there any differences in concentration of serum PRL due to either photoperiod or age after TRH stimulation in Experiment 2. Weight gain of cows did not differ due to photoperiod in Experiment 1 although heifers exposed to 24L:0D gained more weight than those exposed to 18L:6D. Cows in Experiment 2 gained significantly more weight when exposed to 18L:6D. No difference in weight gain due to photoperiod was observed for heifers in Experiment 2. We conclude that milk yield in mature cows can be increased by using supplemental lighting during winter months when compared to natural photoperiod. No differences between 18L:6D and 24L:0D were observed. Prolactin does not appear to be involved in the mechanism of action of photoperiods stimulation of milk yield. Cost analysis of the above data reveal a $16.06 return on each dollar invested for supplemental lighting. The additional income realized through supplemental lighting may allow the dairyman to reduce herd size and operating costs.
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