Growth and Hormonal Response of Heifers to Various Photoperiods

Abstract

Body growth and dry matter intake were measured in three groups of 16 Holstein heifers exposed to (1) natural, (2) 16 hr light: 8 hr dark (16L:8D) or (3) 24L:0D photoperiods for November 11 to March 10. Average daily gain (ADG) of heifers subjected to 16L:8D was 11 (P less than .05) and 17% (P less than .02) greater than ADG of animals receiving 24L:0D or natural photoperiod, respectively. Heifers subjected to 16L:8D consumed 6.9 and 8.3% more (P less than .01) dry matter per day than did animals exposed to 24L:0D or natural photoperiod, respectively. Yet feed to gain ratio of heifers exposed to 16L:8D was lower than that of heifers exposed to 24L:0D or natural photoperiod. Serum prolactin (PRL) and growth hormone (GH) were measured in six heifers in each treatment group at 30-min intervals, and serum total glucocorticoids were measured at 2-hr intervals over a 6-hr period on December 26, February 6 and March 7. Concentrations of serum PRl remained low (less than 3 ng/ml) regardless of photoperiod treatment; this would be expected, however, because mean ambient temperatures were below 0 C on all sampling days. Serum GH and total glucocorticoids were likewise unaffected by photoperiod treatment. This study demonstrates that an 8-hr period of darkness is necessary to achieve increases in weight gain when Holstein heifers are supplemented with light during the autumn-winter season in Michigan, but the mechanisms whereby photoperiod affects body growth remain unknown.

Effects of evening feeding and extended photoperiod on growth, feed efficiency, live animal carcass traits and plasma prolactin of beef heifers housed outdoors during two Manitoba winters

“…Improved growth performance with extended photoperiod has been reported for cattle exposed to light intensities greater than or equal to 104 lux (Peters et al 1980;Stanisiewski et al 1988;Zinn et al 1986a). Survey results by Reksen et al (1999) indicated that extended photoperiod using low intensity (mean = 36 lux, range = 4 to 160 lux) light increased milk production of dairy cows.…”

“…Why this was not the case for the evening-fed EP treatment is not known. Peters et al (1980) found that EP improved heifer growth in a cold environment without a concomitant effect on plasma PRL. Thus, the importance of the PRL response to light is under question.…”

“…Similarly, Small et al (2002) found an inconsistent plasma PRL response to EP (400 lux) in beef heifers housed outdoors during a Canadian winter. Peters et al (1980) and Peters and Tucker (1978) concluded that the effect of EP on plasma PRL might not be sustained when the ambient temperature is below 0°C. Interplay of ambient temperature and low light intensity may have resulted in unpredictable plasma PRL responses to EP in our study, but not that of Small et al (2002) where light intensity was quite high.…”

Urinary Alkaloid Excretion as a Diagnostic Tool for Fescue Toxicosis in Cattle

“…8,11,20 However, prolactin is highly variable depending on animal gender, reproductive state, 1 day length, 10 season of the year, 14,15 and temperature. 21 Therefore, a more direct diagnostic tool is needed to determine if ergot alkaloids in pasture plants are in fact ingested by the animal.…”

The effect of short and skeleton long photoperiods on the plasma concentrations of prolactin and cortisol in sheep

“…A similar feature was also noted by Ravault and Ortavant (1977) The pattern of cortisol spikes showed that the main difference between the two photoperiods was in the size of the peaks rather than in their frequency. The mean number of episodes compares closely with that observed by Fulkerson and Tang (1979) Forbes, 1982) and active immunisation against prolactin depresses growth (Ohlson et al, 1981) there has been a report of a photoperiodic effect on growth in cattle in which prolactin was very low due to low environmental temperatures (Peters et al, 1980 …”