| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
|
|
|
|||||||
|
|||||||||
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
ANIMAL PRODUCTION |
Department of Animal and Range Sciences, Montana State University, Bozeman 59717
 |
Abstract |
|---|
 Top Abstract INTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
|---|
and fixed-time AI (TAI). This was a composite analysis of 3 experiments that evaluated (1) the effects of bull exposure at different days after calving (yr 1); (2) the biostimulatory effects of bull excretory products (yr 2); and (3) the biostimulatory effects of familiar and unfamiliar bulls (yr 3) on the resumption of ovarian cycling activity. In all studies, cows were exposed (biostimulated; n = 94) or not exposed (nonbiostimulated; n = 67) to bulls or excretory products of bulls for at least 60 d before the beginning of the estrus synchronization protocol. Average calving day did not differ among years and was 52 ± 5 d. Year did not affect the proportions of biostimulated and nonbiostimulated cows that were cycling at the beginning of the estrus synchronization protocol; however, a greater (P < 0.001) proportion of biostimulated than nonbiostimulated cows were cycling at this time. In each year, cows were given GnRH followed by PGF2 7 d later. Cows were observed for estrus twice daily (am and pm) after PGF2. Cows that exhibited estrus before 54, 60, and 64 h after PGF2 were inseminated by AI 12 h later in yr 1, 2, and 3, respectively. Cows that failed to show estrus were given GnRH and TAI at 62, 72, and 72 h after PGF2 in yr 1, 2, and 3, respectively. Conception rates were determined by transrectal ultrasonography 35 d after TAI in each year. The percentages of cows that exhibited estrus after PGF2 and before TAI, the interval from PGF2 to estrus, and the percentages of cows inseminated 12 h after estrus or at TAI did not differ between biostimulated and nonbiostimulated cows and were 51%, 54.7 ± 7.3 h, 35%, and 65%, respectively. Conception rates for cows bred by AI 12 h after estrus did not differ between biostimulated and nonbiostimulated cows; however, the TAI conception rate was greater (P < 0.05) for biostimulated cows (57.6%) than for nonbiostimulated cows (35.6%). We conclude that TAI conception rates in an estrus synchronization protocol that includes GnRH followed 7 d later by PGF2 may be improved by the biostimulatory effect of bulls in postpartum, primiparous cows.
Key Words: biostimulation • bovine • estrus synchronization • fixed-time artificial insemination • postpartum • conception rate
|
INTRODUCTION |
|---|
|
TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
|---|
). This problem can create a challenge to estrus synchronization protocols and AI in primiparous cows (Yavas and Walton, 2000; Rhodes et al., 2003). Using estrus synchronization protocols that incorporate fixed-time AI (TAI) allows a majority of cows to be inseminated artificially in a short time. However, in suckled beef cows and dairy cows, GnRH-based estrus synchronization protocols are more successful if postpartum cows have resumed cycling (Geary et al., 2001; Jordan et al., 2002).
One management strategy that has the potential to increase the proportion of primiparous cows that resume cycling is the use of the biostimulatory effect of bulls. The presence of bulls decreased the postpartum interval to estrus and increased the number of primiparous cows that cycled before the beginning of the breeding season (Custer et al., 1990; Fernandez et al., 1993; Fike et al., 1996). Furthermore, conception rates after a 21-d AI breeding season were greater for cows exposed to bulls than for cows not exposed to bulls before the breeding season (Berardinelli, 1987; Fernandez et al., 1993). There are no reports in the literature that have evaluated whether estrus synchronization responses and AI conception rates of postpartum, primiparous cows can be altered by the biostimulatory effect of bulls.
The objective of this study was to evaluate whether exposing primiparous, suckled beef cows to the biostimulatory effect of bulls alters breeding performance associated with an estrus synchronization protocol that included GnRH, PGF2, and TAI. The hypotheses tested were that the proportions of cows that exhibit estrus after PGF2 and AI conception rates do not differ between cows exposed or not exposed to the biostimulatory effect of bulls before the breeding season and during the estrus synchronization protocol.
|
MATERIALS AND METHODS |
|---|
|
TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
|---|
Animal care, handling, and protocols were approved by the Montana State University Large Animal Institutional Animal Care and Use Committee.
One-hundred sixty-one spring-calving, 2-yr-old, Angus x Hereford crossbred, primiparous beef cows were used in this study conducted over a 3-yr period at the Montana State University Livestock Teaching and Research Center in Bozeman. In each experiment (year), cows were stratified by calving date, calf birth weight, sex of calf, and BCS before they were assigned to treatments. Average day of the year that calving occurred was 52 ± 5 d over all of the years. For purposes of this study, cows that were exposed to the physical presence of bulls or exposed to excretory products of bulls were designated as the biostimulated treatment, whereas cows not exposed to bulls or excretory products of bulls were designated as the nonbiostimulated treatment.
The following is a brief description of the experimental designs and treatments for each of the experiments; detailed descriptions of these experiments and the criteria for assessing resumption of ovulatory activity are given in Berardinelli and Joshi (2005a,b) and Berardinelli et al. (2005). Changes in progesterone concentrations in samples collected at 3-d intervals throughout the experimental periods were used to assess the resumption of ovarian cyclicity. An increase in baseline progesterone concentrations that exceeded 1.0 ng/mL in 3 consecutive samples during the experimental period was used as the criterion for resumption of ovarian cycling activity in each year.
Year 1. Fifty-six cows were assigned randomly to be exposed or not exposed to bulls between d 15 and 55 after calving. Four 2-yr-old, epididymectomized Angus bulls were used in this experiment. The bull to cow ratio for each treatment combination that included bull exposure was approximately 1:9. Cows were in their respective treatments for 62 ± 2 d at the beginning of the estrus synchronization protocol.
Year 2. Sixty-two cows were assigned randomly to 1 of 4 treatments: exposed continuously to presence of a bull or excretory products of bulls, and not exposed to a bull or exposed to excretory products of cows beginning on d 35 ± 2 d after calving. Five 3-yr-old, epididymectomized Angus bulls were used in this experiment. Cows exposed to bulls, excretory products of bulls, and excretory products of cows were considered as a single treatment (i.e., biostimulated), and cows not exposed to these factors were considered nonbiostimulated for the purposes of the current study. The bull to cow ratio for cows exposed to bulls was approximately 1:15. Cows exposed to excretory products of bulls or cows were placed into an enclosure that was approximately one-third (~245 m2) of the area of the pen and was used to alternately house bulls and cows. Bulls (n = 4) were placed into this enclosure at approximately 0800 and removed at 1830. Cows were then moved into the enclosure overnight between 1830 and 0800. Cows had been in their respective treatments for 63 ± 2 d at the beginning of the estrus synchronization protocol.
Year 3. Fifty cows were assigned randomly to 1 of 2 treatments: exposure to bulls or exposure to mature, ovariectomized cows from 5 to 35 d after calving. On d 30, 12 cows exposed to familiar bulls were assigned randomly to be exposed to unfamiliar bulls; likewise, 12 cows exposed to familiar ovariectomized cows were assigned randomly to be exposed to unfamiliar ovariectomized cows. The bull to cow and ovariectomized cow to cow ratio was approximately 1:12 during the first 5 to 35 d after calving and then 1:6 for the remainder of the experiment. Cows were exposed to familiar bulls or ovariectomized cows for 95 ± 4 d before the beginning of the estrus synchronization protocol or 60 ± 3 d for cows exposed to unfamiliar bulls or cows before the beginning of the estrus synchronization protocol.
Lots Used for Exposure
The same 2 lots were used in each experiment, designated north and south by their geographic location. Each lot contained four 41 x 18 m (length x width) pens that were similar in east-west configuration, bunk space, aspect, slope, and connection to open-shed shelters. The lots were approximately 0.35 km apart. Animals housed in one lot were not able to see animals in the other lot. In a preliminary experiment involving estrual cows and bulls, there was no indication that animals in either lot were influenced by odorants of animals in the other lot. However, there was a possibility that sounds made by animals in one area could be heard by animals in the other area. Pens within each lot were isolated from each other by draping and securing tarpaulins over the 3-m fences that separated pens. Cows exposed to bulls had no contact with bulls throughout pregnancy and after calving until they were placed into pens with bulls (yr 1, 2, and 3) or excretory products of bulls (yr 2). Cows not exposed to bulls had no contact with bulls throughout pregnancy and the experiments.
Nutrition
Cows and calves had free access to good quality, mixed-grass alfalfa hay and any pasture grasses that were available before they were moved into their respective pens. Once cows were moved into the pens, they were given free access to the same hay (chopped), 0.25 kg of cracked barley per animal daily, water, and a mineralized-salt supplement until the end of the experiment in each year. The TDN and CP of this diet were 58.5 and 7.4%, respectively, on a DM basis and fed to exceed the NRC requirement for lactating beef cows with a mature weight of 545 kg by approximately 18% (NRC, 1996). Bulls were fed the same diet as the cows.
Estrus Synchronization Protocol and AI
The estrus synchronization protocol used in these studies was a combination of the Select Synch and CO-Synch protocols, known as the Hybrid-Synch (Lemaster et al., 2001). On May 18 of each year, each cow was injected i.m. with GnRH (100 µg/cow; d 
), followed by an i.m. injection of PGF2 (25 mg/cow; d 0) 7 d later. Cows were observed for estrus twice daily (0700 and 1900) after injection of GnRH until TAI. Cows that exhibited estrus before 56 (yr 1), 60 (yr 2), or 64 (yr 3) h after PGF2 were inseminated artificially 12 h later by 1 of 2 experienced AI technicians assigned randomly to a cow. Within each year, cows were inseminated with frozen semen from a single sire of known fertility. Cows that failed to show estrus or that were in estrus at the following times were given a second injection of GnRH (100 µg/cow) and TAI at 62, 72, or 72 h after PGF2 for yr 1, 2, and 3, respectively. The reason for the 8-h difference between yr 1 and yr 2 and 3 for TAI was to increase the number of cows that were inseminated 10 to 12 h after estrus because cows were beginning to show estrus at 60 to 64 h after PGF2 in yr 1. In yr 1, bulls were removed from cows at TAI; in yr 2, cows remained in their treatments for 5 d after TAI; and in yr 3, cows remained in their treatments for 7 d after TAI. Cows were exposed to fertile bulls for natural service 20 d after TAI in each year. Conception rates were determined 35 d after TAI by transrectal ultrasonography of the contents of the uterus of each cow.
Statistical Analyses
Calving date, calf birth weight, calf sex ratio, cow BW, and BCS at the beginning and end of each experiment, change in cow BW and BCS (difference between BW and BCS at the beginning and end of each experiment), and interval from PGF2 injection to estrus were analyzed by separate ANOVA for a completely random design (PROC GLM, SAS Inst. Inc., Cary, NC). The model included treatment (biostimulated and nonbiostimulated), year (1, 2, 3), and their interaction. Means were evaluated with the PDIFF option of SAS.
The proportions of cows among treatments that exhibited resumption of ovarian cycling activity by the beginning of the estrus synchronization protocol, estrous response after PGF2, proportions of cows inseminated at 12 h after estrus, proportions of cows inseminated at TAI, conception rates for AI at 12 h after estrus, conception rates for TAI, and overall AI conception rates among years were analyzed separately with PROC CATMOD of SAS. The model for each analysis included year, treatment, and the year x treatment interaction. Data for cows that exhibited estrus after the first GnRH injection and before injection of PGF2 were excluded from these analyses. If year and the interaction of year with treatment were not statistically different (P > 0.10), the data were pooled and reanalyzed using only treatment as the independent variable. The rationale for pooling of data across year is the following: (1) the estrus synchronization protocols were identical in each year; (2) the estrus synchronization protocol began on the same calendar date for each year of these experiments; (3) the same estrus synchronization protocol was employed in each experiment, except for minor differences in the timing of the second GnRH injection and TAI after PGF2 in yr 1; (4) the AI technicians used for these experiments were the same individuals for all 3 yr; and (5) semen was from the same bull within year. Lastly, even though the biostimulatory stimuli were presented to the cows in different ways over these 3 yr, the results were the same. The idea herein was to evaluate the biostimulatory effect, whether it was delivered by a bull or by the excretory products of bulls.
|
RESULTS |
|---|
|
TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
|---|
in yr 1, 2, and 3, respectively; data from these were removed from subsequent analyses.
There was no effect of the interaction between treatment (biostimulated and nonbiostimulated) and year (1, 2, and 3) on percentages of cows cycling at the beginning of the estrus synchronization protocol, percentages of cows exhibiting estrus after PGF2, interval from injection of PGF2 to estrus, percentages of cows that were inseminated 12 h after estrus or bred at TAI, conception rates for AI at 12 h after estrus, TAI conception rates, and overall AI conception rates. Therefore, data for these variables were pooled across years and reanalyzed.
A greater (P < 0.001) proportion of biostimulated than nonbiostimulated cows was cycling at the beginning of the estrus synchronization protocol (Table 1). Proportions of cows that exhibited estrus after PGF2 and before TAI, interval from PGF2 to estrus, and percent-ages of cows inseminated 12 h after estrus or at TAI did not differ between biostimulated and nonbiostimulated cows (Table 1). Artificial insemination conception rates for cows inseminated 12 h after estrus did not differ between biostimulated and nonbiostimulated cows. Of the 35 biostimulated cows that were inseminated 12 h after estrus and before the second GnRH injection, 4 cows had not resumed luteal activity before the beginning of the estrus synchronization protocol, and 31 had resumed luteal function. Conception rates for these cows were 100 and 83.3%, respectively. Of the 22 nonbiostimulated cows that were inseminated 12 h after estrus and before the second GnRH injection, 14 cows had not resumed luteal activity before the beginning of the estrus synchronization protocol, and 8 had resumed luteal function. Conception rates for these cows were 85.7 and 75.0%, respectively. There were no differences in these conception rates among biostimulated and non-biostimulated cows that had or had not resumed luteal function by the beginning of the estrus synchronization protocol.
|
). Likewise, the overall AI conception rate was greater (P < 0.05) for biostimulated cows than for nonbiostimulated cows (Table 1). |
DISCUSSION |
|---|
|
TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
|---|
and TAI. The current study represents a compilation of breeding performance data collected over a 3-yr period from individual experiments that evaluated factors related to the biostimulatory effect of bulls. There were differences in the design of the experiments and in presentation of the biostimulatory effect of bulls. However, the response of postpartum, anovulatory cows to the biostimulatory effect of bulls or the excretory products of bulls or cows was similar over the 3 yr, as indicated by the absence of a treatment x year interaction.
The biostimulatory effect of bulls before and throughout the course of the estrus synchronization protocol employed in the current study did not appear to alter the percentages of cows exhibiting estrus after PGF2 or interval from injection of PGF2 to estrus of primiparous cows that showed estrus before TAI. An explanation of these results may be that observations for behavioral estrous behavior ended at TAI (62, 72, and 72 h after PGF2 for yr 1, 2, and 3, respectively) and there were only 35 and 22 biostimulated and nonbiostimulated cows, respectively, that had exhibited estrus by TAI. The truncation of observations for estrus may have led to this result.
Conception rates for cows inseminated 12 h after estrus did not differ between biostimulated and nonbiostimulated cows. These results indicate that when combined with the Hybrid-Synch protocol used in this study, the biostimulatory effects of bulls do not improve AI conception rates of cows inseminated 12 h after a synchronized estrus.
Overall AI conception rate for biostimulated cows was greater than that for nonbiostimulated cows. This advantage appears to be a direct reflection of the significant difference in TAI conception rates between biostimulated and nonbiostimulated cows (57.0 and 36.4%, respectively). An explanation for this result is not obvious. There were more biostimulated cows cycling before the beginning of the synchronization protocol than non-biostimulated cows. Artificial insemination conception rates after a GnRH-based estrus synchronization protocol are greater for cycling cows than for anovular cows (Geary et al., 1999; Thompson et al., 1999; Lemaster et al., 2001). Thus, the likelihood of increased conception rates to TAI would be greater for biostimulated cows. On the other hand, there may have been many fewer nonbiostimulated cows that were physiologically able to respond to the first or second GnRH injection. Those that responded to the first GnRH injection exhibited estrus and were inseminated 12 h later. One could hypothesize that the few remaining physiologically capable nonbiostimulated cows responded to the second GnRH injection and became pregnant to TAI leaving a large proportion of nonresponsive nonbiostimulated cows that would be incapable of becoming pregnant to TAI. This hypothesis may be supported by data of Lamb et al. (2001), who reported that pregnancy rate for anestrous cows given 2 injections of GnRH, one 7 d before PGF2 and the other 48 h later, was only 39% (22 of 56 cows). Another possible explanation for these results may be that nonbiostimulated cows may have had greater embryonic mortality than biostimulated cows after TAI. Lastly, it may simply be that the biostimulatory effect of bulls before the beginning of and during the estrus synchronization protocol increases TAI conception rates by enhancing the number of cows that will respond to the second GnRH injection.
Evidence suggests that the biostimulatory effect of bulls and cows on resumption of ovulatory activity in postpartum beef cows is related to a pheromonally mediated mechanism. The biostimulatory pheromone appears to be carried in the excretory products of bulls (Berardinelli and Joshi, 2005b) or cervical mucus of estrual cows (Wright et al., 1994). Thus, the possibility exists that biostimulatory pheromone(s) of bulls or cows may not only affect resumption of ovulatory activity in postpartum, anestrous cows but may also influence breeding performance by directly affecting the ovary or reproductive tract physiology to enhance TAI conception rates in GnRH-responsive cows. These concepts require further investigation.
Use of estrus synchronization protocols and TAI has clear benefits in beef cattle reproductive management strategies. However, the efficacy of estrus synchronization protocols that employ GnRH, PGF2, and TAI is limited by the number of postpartum cows that have resumed ovulatory activity. The biostimulatory effect of bulls provides an efficient and sustainable means to increase the number of postpartum cows that are cycling before the implementation of this type of estrus synchronization protocol and AI program. Furthermore, the biostimulatory effect of bulls appears to enhance TAI conception rates in an estrus synchronization protocol that includes GnRH followed 7 d later by PGF2 and GnRH given at TAI.
|
Footnotes |
|---|
2 Presented in part at the 56th Annual Meeting of the West. Sect. of the Amer. Soc. of Anim. Sci., Las Cruces, NM, June 2005.
4 Current address: The Ohio State University, 185 Hamilton, 1645 Neil Ave., Columbus, OH 43210.
3 Corresponding author: jgb{at}montana.edu
Received for publication December 26, 2005. Accepted for publication October 29, 2006.
|
LITERATURE CITED |
|---|
|
TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
|---|
for ovulation control in postpartum suckled beef cows. J. Anim. Sci. 79:2253–2259. for estrus synchronization in cattle of Bos indicus breeding. J. Anim. Sci. 79:309–316.. J. Anim. Sci. 77:1823–1832.This article has been cited by other articles:
|
|
 |
|
  S. A. Tauck and J. G. Berardinelli Putative urinary pheromone of bulls involved with breeding performance of primiparous beef cows in a progestin-based estrous synchronization protocol J Anim Sci, July 1, 2007; 85(7): 1669 - 1674. [Abstract] [Full Text] [PDF]
|
|
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
