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Dairy Cattle
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FULL TEXT PAPER
Production Response to Subcutaneous BST Injections in the Neck Versus Tail Head in Holstein Cows
by Richard L. Wallace, Douglas A. Hilgendorf, and James A. Campbell


TAKE HOME MESSAGES

  • BST injections under the skin of the neck significantly increased milk production in early and late lactation cows, as well as first and second or greater lactation cows.
  • An additional 2-5 pounds of milk per day for up to 10 days post injection could cover any potential increase in labor.

METHODS

Cows housed in the free stall barns at the University of Illinois Dairy Cattle Research Unit typically receive BST injections in the tail head. Every 14 days, the injection site is switched from the left to the right side. One hundred thirty three cows who had previously been injected with BST in the tail head one or more occasions were eligible to enroll. Cows were stratified based on days in milk, then randomly allocated to one of two treatment groups so that the average days in milk would be similar between groups. One group of cows (n=68) was assigned to receive BST injections in the neck (N) while the second group of cows (n=65) was assigned to continue receiving BST injections in the tail head (T). On BST injection date (Oct. 9, 2002), the cows were restrained at the feed bunk in lockups and given injections according to assigned group.

Mean lactation number (LN), days in milk (DIM), most recent DHIA milk production (DMP), most recent somatic cell score (SCS), days carried calf (DCC), and body condition score (BCS) were obtained or determined. For these measures, a T-test for independent groups was used to evaluate statistical differences between groups. Daily milk production from the nine days prior to subsequent BST injection (the initial injection comparing neck versus tail head sites) was collected. Daily milk production was followed for 14 days after the trial dose of BST was administered. Repeated measures analysis of variance RM-ANOVA was used determine if there was a significant difference between treatments.

RESULTS

There was no statistical difference between treatment groups N and T for mean LN (1.97, 1.99; p=0.95), mean DIM (210, 216; p=0.40), mean DMP (72.9, 70.9; p=0.80), mean SCS (3.8, 4.2; p=0.16), mean DCC (73, 79; p=0.46) and mean BCS (3.1, 3.0; p=0.39). Pregnancy status for every cow had not been established, so mean DCC was calculated with only confirmed cows. Using RM-ANOVA, daily milk production by treatment group for the nine days prior to BST injection (Oct. 1 to Oct. 9) was not found to be significantly different (F=0.49; p=0.86). Daily milk production for the next 14 days post injection (Oct. 10 to Oct. 23) was found to be significantly different between treatment groups (F=6.06; p<0.001).

Analysis was also performed by evaluating production from cows less than or greater than 200 DIM and from first versus second or greater lactation cows. The relationships between treatment groups (N vs T) are shown in the following graphs. In each instance, there was no significant difference in milk production for the nine days prior to BST injection, while there was a significant difference after injection.







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