Int J Biometeorol (1989) 33:89-94 meteorology Effect of supplemental light on growth, prolactin, progesterone and luteinizing hormone in water buffalo (BubMus bubalis) K.S. Perera*, F.C. Gwazdauskas, R.M. Akers, and M.L. McGilliard Department of Dairy Science, College of Agriculture and Life Sciences, Virginia Agricultural Experiment Station, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061, USA Abstract. Fifty non-pregnant Surti buffalo heifers aged between 17 and 42 months (n=24, <24 months; n =26, >24 months) were randomly as- signed to groups subject to either natural daylight +4 h supplemental light (n=25) or natural day light (n=25), to study changes in growth, serum prolactin (Prl), progesterone (P4) and luteinizing hormone (LH) to supplemental lighting. Ambient temperatures (T) and relative humidity (RH) gen- erally were >27~ and <70% during the day- time, respectively. Light-supplemented heifers had 6.2 kg net body weight (BW) gain at 9 weeks com- pared to 20.8 kg for controls, but higher mean Prl after 6.5 weeks (P<0.01), and higher P4 (0.41 vs 0.19 ng/ml; P<0.06) than control heifers. Older heifers had 39.7% greater BW (P<0.01), but a net 4.3% BW gain compared to a 10.1% gain for younger heifers at 10 weeks. Older, light-supple- mented heifers had higher mean P4 (0.63 vs 0.19 ng/ml; P < 0.07) than the other groups. These weight and hormonal changes suggest that 4 h sup- plemental light can alter growth and endocrine function in buffaloes under similar planes of nutri- tion. While light supplementation did not have a positive effect on body weight during the 10 week study, body weight and endocrine changes due to supplemental light may be important factors for initiation of reproductive cyclicity. Key words: Water buffalo - Supplemental light- Prolactin - Progesterone - LH Introduction Buffalo attain puberty at an older age than cattle (Jain and Pandey 1985; Singh and Singh 1985; * Present address: Department of Animal Science, University of Peradeniya, Peradeniya, Sri Lanka Offprint requests to." F.C. Gwazdauskas Tulloch and Grassia 1981). Although sufficient data are not available to completely understand regulation of the onset of puberty of the water buffalo, similarity of buffalo and cattle reproduc- tive tract anatomy (Aboule-Fadle et al. 1974; Mo- barak 1969) and endocrine physiology (Arora and Pandey 1982; Batra and Pandey 1983; Kanai and Shimizu 1984; Dobson and Kamonpatana 1986) make it probable that factors which modify the pubertal onset in cattle exert similar effects on sex- ual maturity of buffaloes. Two factors which affect the onset of puberty of cattle are nutrition (Short and Bellows 1971; Sorensen et al. 1959) and photoperiod (Peters et al. 1978; Petitclerc et al. 1983 a, b). Most buffalo rear- ing countries' current conditions preclude immedi- ate improvement in the plane of nutrition. How- ever, improvement in reproductive efficiency may be possible by changes in management. Supple- mental lighting of 16 h per day when day length was less than 13 h improved the growth rate (Peters et al. 1978, 1980) and hastened the sexual maturity of prepubertal heifers even under condi- tions of low planes of nutrition (Petitclerc et al. 1983b). In tropical countries such as Sri Lanka, where natural day length does not exceed 13 h and the plane of nutrition for livestock is low, such manipulation of the photoperiod could be similarly beneficial, but data for the buffalo are lacking. This study was designed to measure changes in the concentrations of prolactin (Prl), progesterone (P4) and luteinizing hormone (LH) in serum, and in the weight of Surti buffalo heifers subjected to 4 h of supplemental lighting under tropical condi- tions. Materials and methods The study was conductedat the National LivestockDevelop- ment Board Farm, Melsiripura, Sri Lanka, between July 10