Responses in venison production to grazing pastures based upon perennial ryegrass or annual ryegrass and to immunisation against melatonin

A.M. Ataja, P.R. Wilson, J. Hodgson, R.W. Hoskinson, R.W. Purchas, H. Varela-Alvarez, T.N. Barry

Massey University, Palmerston North

Proceedings of the New Zealand Society of Animal Production. 1990, 50: 279-286

During 1989, two groups of weaner red deer stags (n=18) grazed either perennial ryegrass (PRG) or Moata annual ryegrass (ARG) based pastures from mid-May until the end of November. Within each group, animals (n=6) were either not immunised or immunised against melatonin using Freund's or Dextran adjuvants. Treatment effects upon winter (W) and spring (S) LWG, proportion of animals attaining target liveweight (93kg; 50kg carcass weight by November 30), pasture composition, voluntary DM intake (VFI), anti-melatonin titres and plasma prolactin concentrations were determined.

During winter, LWG (165 v 140 g/day; P<0.05) and VFI (1.62 v 1.20 kg DM/day; P<0.001) were greater for animals grazing ARG than PRG pastures, resulting in a greater proportion of deer attaining the target slaughter weight (60 v 41%). Organic matter digestibility and N content were higher (P<0.05) for the ARG than PRG pastures during winter. Maximum anti-melatonin titres of 1:15,215ą5, 551 (SE) and 1:1,941 ą 423 were attained in October and May respectively for the Frecund's and Dextran adjuvant groups. Plasma prolactin concentrations were higher for immunised than for control animals during W and S. Growth to 6 months of age was depressed in stags immunised using Freund's adjuvant. There was evidence that immunisation using Dextran increased growth from 9-12 months of age, but this did not attain significance (P>0.05).

Keywords: NZSAPAB; Red deer; LWG; VFI; melatonin antibody titre

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