La. Burgwaldbalstad et al., INFLUENCE OF FORAGE LEVEL AND NALOXONE INJECTION OF FEED-INTAKE, DIGESTION, AND PLASMA-HORMONE AND METABOLITE CONCENTRATIONS IN DAIRY HEIFERS, Journal of animal science, 73(9), 1995, pp. 2677-2686
Four ruminally cannulated Holstein heifers (287 +/- 26 kg) in a 4 x 4
Latin square were used to evaluate the effects of naloxone injection a
nd forage level on dietary intake, ruminal fermentation characteristic
s, digestibility, and plasma hormone and metabolite concentrations. Tr
eatments were arranged in a 2 x 2 factorial with naloxone injection (0
vs .3 mg/kg; saline us naloxone, respectively) and forage level (20 v
s 100%; concentrate vs forage) as factors. Stanchioned heifers were al
lowed 21 d for adaptation before a 5-d collection period. Plasma sampl
es were collected several times on d 1 and daily at 0730. Concentrate-
fed heifers consumed more feed (P < .10) than forage-fed heifers. Nalo
xone injection decreased (P < .10) feed intake (grams/kilogram BW) at
1 and 2 h after feeding on d 1. On d 3 at 24 h after feeding, naloxone
-injected heifers had increased DM (P < .10) intakes compared with con
trol (saline-injected) heifers. Concentrate-fed heifers had decreased
(P < .10) ruminal pH and increased total ruminal VFA concentration. Ac
etate proportion was decreased (P < .10) and propionate proportion inc
reased in concentrate-fed heifers. Naloxone-injected heifers had decre
ased (P < .10) total VFA concentrations and increased propionate propo
rtions. Concentrate-fed heifers had greater (P < .10) DM, OM, and CP d
igestibilities as well as increased plasma (P < .10) insulin, urea N,
and glucose concentrations but decreased (P < .10) GH and NEFA concent
rations. Naloxone injection increased (P < .10) plasma insulin concent
ration. Naloxone injection in dairy heifers reduces intake up to 2 h a
fter injection, alters ruminal fermentation patterns, and increases pl
asma insulin concentration.