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Controlling First Service and Calving Interval by Prostaglandin F2e, Gonadotropin-Releasing Hormone, and Timed Insemination 1 M A T T H E W C. LUCY, 2 JE F F R E Y S. STEVENSON, 3 and E. P. C A L L Department of Animal Sciences and Industry Kansas State University Manhattan 66506

ABSTRACT

rate approached that of controls (51%). Methods of timed insemination utilized and their resulting low conception rates prevented a true test of the utility of estrous synchronization to reduce duration and variability of calving intervals, even though variability of intervals to first service was reduced.

Our objective was to determine if calving intervals could be shortened and made less variable by using prostaglandin F2~ to control the occurrence of first services. Holstein cows (n=348) were assigned at calving to four treatment groups. Control cows (n=88) were inseminated at their first observed estrus after 40 d postpartum. Estrous cycles of the remaining cows were synchronized with prostaglandin F2a to allow insemination (first services) 80 h after the second injection (n=86), insemination at 80 h preceded by gonadotropin-releasing hormone at 72 h (n=86), or insemination at 72 and 96 h (n=88) after the second injection (51 to 57 d postpartum). By design, interval to first service was reduced to 57 d for treated cows (63 d for controls) and was less variable (12% of that for controls). Conception rate at first service was lower after timed inseminations than that of controls. Intervals to conception and subsequent calving were similar in all treated cows and controls. Of cows sampled, 23 of 176 (13%) failed to respond with luteolysis when progesterone in serum exceeded 1 ng/ml, and 26 of 176 (15%) had low concentrations of progesterone in serum and could not respond to prostaglandin F2~. Poor response to timed inseminations may have occurred because only 72% of 176 cows sampled responded with luteolysis. When only cows observed in estrus were considered, conception

INTRODUCTION

Received February 7, 1986. 1Contribution Number 86-283-J, Kansas Agricultural Experiment Station. Department of Animal Science, North Carolina State University, Raleigh. 3 Reprint requests. 1986 J Dairy Sci 69:2186-2194

Calving interval has profound economic effects in the dairy herd (5, 14). Numerous studies have demonstrated the benefit of a 12 to 13-too calving interval (1, 5, 8, 14, 19). Inte~als longer than optimum result when cows spend a greater proportion of their lactation in the less profitable part of their lactation curve (5). Thus, economic losses associated with prolonged calving intervals often go undetected by dairy producers, because they represent lost potential income and not cash outlay (5). Estrous detection and interval to first service are the most important factors affecting calving interval (15). Poor estrous detection has been linked to reproductive inefficiency in many studies, and its effect on calving interval is well-documented (2, 3, 15). Interval to first service has received less attention than estrous detection as a measure of reproductive performance. Furthermore, calving interval and interval to first service are highly correlated (4, 10, 18), and optimal calving intervals may be unattainable without decreasing intervals to first service (5). Unfortunately, reducing calving intervals to an optimal average on a herd basis does not optimize necessarily individual calving intervals for all cows in the herd. The herd average can include cows with extremely short or extended intervals. Reducing interval to first services will shorten calving intervals (10, 20), but postpartum inseminations earlier than 60 d m a y lower conception rates (4). An option through estrous

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CONTROLLING FIRST SERVICE AND CALVING INTERVAL synchronization is to schedule all first services at approximately 60 d in an attempt to shorten the duration and variability of calving intervals. Our objectives were 1) to determine if duration and variability of calving intervals could be reduced by controlling time of first services with prostaglandin F2a (PGF); 2) to evaluate the reproductive performance of dairy cows subjected to three treatments using timed insemination after PGF and gonadotropinreleasing hormone (GnRH); and 3) to assess efficacy of PGF-induced luteolysis and estrus and its subsequent effect on the success of timed inseminations. MATERIALS A N D METHODS Experimental Design

Lactating Holstein cows (n=348) from the Kansas State University dairy herd that calved between July 1, 1983 and June 30, 1985 were utilized. Cows were housed in a freestall confinement facility exposed to the environment. The diet consisted of a concentrate mix (16% protein) containing 50% corn and 50% sorghum grains, soybean meal, 1.5% sodium bicarbonate, and minerals in a self-feeder and alfalfa hay fed ad libitum. Cows were milked twice daily at 0930 and 2130 h. Two daily 30-min observations (0700 to 0900 h and 1600 to 1800 h) were conducted for estrous detection. A t calving, cows were assigned to four treatment groups. Control cows (n=88) were inseminated artificially (AI) at first observed estrus after 40 d postpartum. Time of first services was scheduled in the remaining cows using two 25-mg i.m. injections of PGF (PGF-1 and PGF-2; Lutalyse®; The Upjohn Company, Kalamazoo, MI) 11 d apart. Small groups of cows were treated together on Thursdays of each week (0800 to 0900 h) when cows were 40 to 46 d postpartum. Eleven days later (Mondays), cows were given a second injection (PGF-2) between 0800 and 0900 h. Following PGF-2 (0 h), cows were treated according to the following procedures: 1) AI at 80 h (n=86); 2) 100 /ag (i.m.) GnRH (Cystorelin ®, CEVA Laboratories, Overland Park, KS) at 72 h and A1 at 80 h (n=86); or 3) AI at 72 and 96 h (n=88). Injections of GnRH occurred on Thursdays (0800 to 0900 h), 80-h inseminations on Thursday afternoons (1600 to 1700

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h), and 72 and 96-h inseminations on Thursday and Friday mornings (0800 to 0900 h). Inseminations at 72 and 96 h were counted as one service. Cows were reinseminated according to observed estrus until determined pregnant by uterine palpation per rectum at 40 to 46 d after AI or removed from the herd for various reasons including infertility. Blood Collection

Blood was collected by coccygeal venipuncture from a random group of PGF-treated cows (n=176) at 0 and 48 h after PGF-1 and PGF-2. Samples were stored at 5°C for 24 h until serum was harvested b y centrifugation. Samples of serum were held at - 2 0 ° C until assayed for progesterone (P) by radioimmunoassay (21). lntraassay a n d interassay coefficients of variation were 10.3 and 15.1%, respectively. A luteolytic response after PGF-2 was indicated when P in serum exceeded 1 ng/ml at 0 h and was less than 1 ng/ml at 48 h. No luteolysis was indicated when P was greater than 1 ng/ml at 0 and 48 h after PGF. Serum P of less than 1 ng/ml at 0 and 48 h suggested that cows did not have a functional corpus luteum. Statistical Analyses

A different inseminator was used during the first and second year of the study. Because no effect of inseminator was found, data were combined. Intervals to first service, first service to conception, conception rate at the first three services, calving interval (estimated by adding 280 days to the interval from calving to conception), and services per conception and per cow were analyzed by the least squares procedures of the Statistical Analysis System (17). Treatment (n=4), lactation (primiparous or muhiparous), season of calving (October 1 to January 31, February 1 to May 30, or June 1 to September 30), and all two-way interactions were included as sources of variation. A measure of the variation associated with the mean intervals to first service, to first service conception, and to subsequent calvings was determined by Levene's test (12). This was accomplished by calculating a residual for each observation (absolute value of the difference between the observed value and treatment mean), which was subjected to analysis of variance. When the resulting F-test was significant, Journal of Dairy Science Vol. 69, No. 8, 1986

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LUCY ET AL.

variances were heterogeneous, and synchrony of fit for individual observations about the mean were compared by the relative magnitudes of the residual means for each treatment. Smaller mean residuals indicated less variability within treatment. Orthogonal contrasts were made between treatment means (control vs. timed AI groups, timed AI with and without GnRH, and one vs. two timed inseminations). Selected nonorthogonal contrasts were made by Scheffe's interval (17). Enumeration data (percentages) were tested for independence by chi-square. R E SU L TS Intervals from Parturition to First Service and Conception

Analyses of variance for various reproductive traits are in Table 1. Interval to first service was affected only by treatment as average intervals to first insemination were 6 d shorter (P