HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Abstract Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Looper, M. L. Articles by Wettemann, R. P. Search for Related Content PubMed PubMed Citation Articles by Looper, M. L. Articles by Wettemann, R. P.

Body condition at parturition and postpartum weight changes do not influence the incidence of short-lived corpora lutea in postpartum beef cows¹

Department of Animal Science, Oklahoma Agricultural Experiment Station, Stillwater 74078

	Abstract

Top Abstract Introduction Materials and Methods Results Discussion Implications Literature Cited

 
Seventy-seven multiparous beef cows (Hereford and Angus x Hereford) with thin to moderate BCS at calving were used to evaluate the effects of body condition at parturition and BW change after calving on duration and occurence of luteal activity before and after first estrus. Blood samples were collected twice weekly after parturition to determine the occurrence of the first postpartum luteal activity (LA, progesterone 0.5 ng/mL). Weight changes and BCS were determined at 2-wk intervals. Cows were exposed to bulls and observed twice daily for behavioral estrus. Luteal activity was classified as normal if plasma concentrations of progesterone were 0.5 ng/mL for at least 11 d, or short if concentrations of progesterone were 0.5 ng/mL for 10 d or less. The interval from parturition to first normal LA was shorter (P < 0.001) for moderate condition (BCS 4.5) than for thin (BCS 4) cows (58.3 ± 3.2 vs. 93.3 ± 5.1 d, respectively). Interval to first estrus also was shorter (P < 0.001) for moderate than for thin cows (53.3 ± 3.7 vs. 89.3 ± 5.6 d, respectively). Before the first normal LA, 78% of cows had an increase in progesterone for <11 d. Postpartum weight change and BCS at calving did not influence the incidence of estrus associated with first normal LA. After the first estrus, 72% of cows had normal LA, 16% had a short luteal phase, and 12% lacked LA. Postpartum weight change and BCS did not influence the length of LA associated with the first estrus. Cows with normal LA had increased (P < 0.05) maximal concentrations of progesterone compared with cows that had a short luteal phase. When a transient increase in progesterone occurred before first behavioral estrus, 81% of cows had normal luteal function after estrus. We conclude that when beef cows are in thin to moderate body condition at calving, postpartum BW change and BCS at calving do not influence the duration of luteal activity before or after the first postpartum estrus.

Key Words: Beef Cows • Body Condition • Corpus Luteum • Estrus

	Introduction

Top Abstract Introduction Materials and Methods Results Discussion Implications Literature Cited

 
Resumption of luteal activity in postpartum beef cows resembles the luteal events associated with puberty. Transient increases in progesterone in plasma occur in heifers prior to first estrus (Gonzalez-Padilla et al., 1975; Berardinelli et al., 1979). Similarly, first ovulations after parturition in beef cows are usually followed by a transient increase in progesterone for 4 to 5 d (Williams and Ray, 1980; Humphrey et al., 1983; Perry et al., 1991). A normal luteal phase preceded by estrus often follows this transient increase in progesterone (Perry et al., 1991; Werth et al., 1996). Increased progesterone in plasma after the first ovulation in postpartum beef cows is similar to concentrations of progesterone produced by short-lived corpora lutea formed in cows induced to ovulate by calf separation (Odde et al., 1980; Ramirez-Godinez et al., 1982) or GnRH administration (Kesler et al., 1980; Wettemann et al., 1982). First ovulation in postpartum beef cows may not always be accompanied by behavioral estrus (Graves et al., 1968; Wettemann et al., 1978). Intensity of estrus associated with the early transient increases in progesterone during the postpartum period may be minimal and estrus may not always be observed (Perry et al., 1991; Shipka, 2000).

Reduced nutrient intake during the prepartum period increases the interval from parturition to first estrus in beef cows (Dunn et al., 1969; Bellows and Short, 1978; Richards et al., 1986). Inadequate body energy reserves at parturition increase the days to conception (Richards et al., 1986; Selk et al., 1988). Nutritional effects on the incidence of short-lived corpora lutea in mature beef cows have not been elucidated. The purpose of this study was to evaluate the effect of body condition at parturition and postpartum BW change on duration of the first luteal activity (LA) after calving, and on duration of LA after the first estrus in beef cows.

	Materials and Methods

Top Abstract Introduction Materials and Methods Results Discussion Implications Literature Cited

 
Seventy-seven Hereford and Angus x Hereford cows with moderate to good body condition (BCS = 5.2 ± 0.1; 1 = emaciated, 9 = obese, Wagner et al., 1988) were utilized. Commencing 3.5 mo prior to the initiation of the calving season (mean calving date = April 1; range = February 26 to May 17), cows were randomly assigned to one of two prepartum diets to either maintain a BCS of 5 (moderate) or to lose BCS and become a 4 (thin). All cows grazed native grass range and were fed either 0.68 kg/d (lose) or 1.36 kg/d (maintain) of a 40% CP supplement until parturition. After parturition, all cows grazed native grass range and were fed 1.8 kg/d of a 40% CP supplement until May 15 when adequate forage was available. Body weight changes and BCS were determined at 2-wk intervals. Postpartum weight change was the difference in weight between 10 and 60 d after calving. After calving, cows were classified into one of three postpartum weight change categories: 1) gain (+11.4 to +45.5 kg), 2) maintain (-9.1 to +9.1 kg) and 3) lose (-11.4 to -40.9 kg). Cows were exposed to bulls and observed twice daily (30-min intervals) for behavioral estrus commencing at 30 d after calving until at least 98 d after calving. To aid in detection of estrus, fertile bulls were fitted with chin-ball markers and All-Weather PaintStik (LA-CO Industries, Inc., Elk Grove Village, IL) was applied to the tailhead of cows weekly. Cows were considered to be in estrus when they stood to be mounted by bulls or other cows, or tail paint was rubbed off between observation periods.

Commencing at 30 d after calving, blood plasma samples were collected at 3- or 4-d intervals (Monday and Thursday) into 15-mL tubes containing EDTA (0.1 mL of 15% solution) by venipuncture of the tail, placed on ice, and centrifuged within 2 h (2,500 x g for 15 min). Samples were stored at -20°C until progesterone concentrations were quantified to determine the occurrence of first postpartum LA (progesterone 0.5 ng/mL). Concentrations of progesterone in plasma were quantified by a solid-phase RIA (Coat-A-Count progesterone kit, Diagnostic Products Corp., Los Angeles, CA; Vizcarra et al., 1997). Intra- and interassay CV (n = 22 assays) were 7 and 4%, respectively. Sensitivity of the assay was 0.1 ng/mL. Luteal activity was classified as normal if four consecutive samples had 0.5 ng/mL of progesterone (LA for at least 11 d) or short if three or fewer consecutive samples had 0.5 ng/mL of progesterone.

The effects of BCS at parturition and postpartum weight change on occurrence and duration of LA after estrus were analyzed by least squares ANOVA using the GLM procedure of SAS (SAS Inst., Inc., Cary, NC). Effect of duration of LA on maximal concentrations of progesterone was determined by least squares ANOVA. Means were compared using the PDIFF statement of SAS when protected by a significant (P < 0.05) main effect. Chi-squared analysis (SAS) was used to determine the effect of LA before first postpartum estrus on the duration of subsequent luteal activity.

	Results

Top Abstract Introduction Materials and Methods Results Discussion Implications Literature Cited

 
Body condition score of cows fed to lose condition during pregnancy was less (P < 0.05) at calving than for cows fed to maintain condition (Table 1). During the first 60 d after calving, 28 cows gained BW (+ 23.6 ± 1.6 kg), 20 cows lost BW (-18.6 ± 1.9 kg), and 29 cows maintained BW (+1.0 ± 1.5 kg; P < 0.001). After calving, the number of cows gaining weight was not different (P > 0.1) between thin and moderate condition cows. More thin cows (P = 0.08) maintained weight and fewer thin cows (P < 0.05) lost weight after calving than moderate condition cows. The intervals from parturition to normal LA and to first estrus were shorter (P < 0.001) for moderate BCS cows than for thin cows (Table 1). The interval from parturition to conception was 24 d less for moderate BCS cows than for thin cows (P < 0.05; Table 1). The interval from first normal LA to conception was shorter (6 d, P <0.003) for thin condition vs. moderate cows (16 d).

Estrus was detected in 74% (57/77) of cows during the experiment. Body condition score at parturition and postpartum weight change did not influence the incidence of estrus associated with first normal luteal activity, or the duration of LA associated with first estrus. After the first estrus, 72% of cows had normal LA, 16% had a short luteal phase (one to three consecutive samples with progesterone 0.5 ng/mL), and 12% lacked LA (Table 2). The duration of LA influenced (P < 0.05) maximal concentrations of progesterone (Figure 1).

View larger version (9K): [in this window] [in a new window]   Figure 1. Maximal concentrations of progesterone in postpartum beef cows with different numbers of consecutive blood samples with progesterone 0.5 ng/mL. Blood samples were collected on Monday and Thursday of each week. Duration effect (P < 0.001; pooled SE = 2.15).a,b,cMeans with different superscripts differ (P < 0.05).

	Discussion

Top Abstract Introduction Materials and Methods Results Discussion Implications Literature Cited

Body condition at parturition and postpartum weight change had no effect on the duration of the first postpartum LA or the incidence of normal luteal activity after the first estrus. However, the interval from first normal LA to conception was shorter for cows that were thin at calving than for moderate-condition cows. This could be associated with the greater interval to normal LA after calving (35 d) in thin vs. moderate cows. Luteal phases of reduced length occur in heifers prior to puberty (Berardinelli et al., 1979) and during resumption of LA in postpartum cows (Humphrey et al., 1983; Perry et al., 1991; Ciccioli and Wettemann, 2000).

The source of the first increase in progesterone in plasma at puberty or postpartum is probably of ovarian origin. Increased concentrations of progesterone in heifers prior to puberty are associated with luteal tissue below the surface of the ovary (Berardinelli et al., 1979). Daily ultrasonography of postpartum cows indicated formation of a short-lived CL associated with a transient increase in progesterone (Perry et al., 1991). Luteinization of follicles may account for increases in progesterone since ovarian palpation may not reveal CL formation (Corah et al., 1974; Rawlings et al., 1980).

First normal LA activity was preceded by estrus in 72% of the cows. Graves et al. (1968) found that 42% of nonsuckled beef cows that were observed twice daily for estrus ovulated without exhibiting estrus, whereas 70% of suckled beef cows did not exhibit behavioral estrus associated with the first postpartum ovulation. However, with rectal palpation, the lifespan of the CL was not determined. Ultrasonography and estrus detection thrice daily revealed that 10 of 12 suckled beef cows ovulated without exhibiting behavioral estrus after parturition (Perry et al., 1991), and all had short-lived CL. Concentrations of estradiol in serum prior to ovulation and maximal diameter of the ovulatory follicle were similar at the first (short luteal phase) and second ovulation (normal luteal phase) in suckled beef cows (Perry et al., 1991). Although weaning of calves increases the incidence of short-lived CL (Odde et al., 1980), follicle size was not different between beef cows with calves weaned early and in cows with normal estrous cycles (Braden et al., 1989). Reduced life span of the first postpartum CL is associated with increased concentration of PGF₂ in plasma since hysterectomy increases the lifespan of the first CL and reduces concentrations of PGF₂ in plasma (Edqvist et al., 1978; Copelin et al., 1987).

In the current experiment, behavioral estrus was not detected in 26% of postpartum cows observed for at least 98 d after calving. Intensity of estrous behavior may be reduced in postpartum beef cows. Perry et al. (1991) found that estrous activity was less intense or was absent in postpartum beef cows observed thrice daily. Similarly, the duration of estrus and the number of mounts at the first postpartum estrus in primiparous (Ciccioli and Wettemann, 2000) and mature beef cows (Lents et al., 2000) were reduced compared with nonlactating beef cows (White et al., 2002).

The duration of LA influenced maximal concentrations of progesterone in plasma. Maximal concentrations of progesterone in cows with short luteal activity were 30% that of cows with normal luteal activity. Similarly, concentrations of progesterone associated with a transient increase in progesterone were lower than during normal LA in postpartum, suckled beef cows (Rawlings et al., 1980; Perry et al., 1991; Werth et al., 1996). Decreased maximal concentrations of progesterone associated with a short luteal phase may be due to reduced CL size. Postpartum cows induced to ovulate with GnRH had smaller CL compared with GnRH-treated cows pretreated with progesterone (Rutter et al., 1985). Diameters of the first (short luteal phase) and second (normal luteal phase) CL in postpartum beef cows were similar through d 4 after ovulation (Perry et al., 1991). However, diameters of CL were larger from d 5 to 8 after the second vs. first ovulation. Lents et al. (2000) found that cows with thin BCS (BCS = 4.3) had decreased size of ovulatory follicles at the first postpartum estrus compared with moderate conditioned cows (BCS = 5).

Transient increases in progesterone in postpartum cows may be necessary for resumption of normal LA. Eighty-one percent of cows with a transient increase in progesterone before first estrus subsequently had normal luteal function, and 36% of cows lacking a transient increase in progesterone had normal luteal function after estrus. Conception rates were greater in primiparous beef cows with a transient increase in progesterone before estrus than in cows lacking a transient increase in progesterone (Corah et al., 1974; Werth et al., 1996). Induction of ovulation in postpartum cows with GnRH (Kesler et al., 1980; Pratt et al., 1982) or calf separation (Odde et al., 1980; Ramirez-Godinez et al., 1982) causes abnormal luteal function, which may be eliminated by progesterone treatment prior to GnRH or calf separation (Ramirez-Godinez et al., 1981).

Increased progesterone in plasma before normal LA in postpartum beef cows may stimulate the hypophyseal-hypothalamic-ovarian axis. Gonadotropin stores in the pituitary gland are diminished at parturition due to prolonged exposure to increased concentrations of steroids during gestation (Chamley et al., 1976; Moss et al., 1980). Increased secretion of LH occurs after progesterone treatment of anestrous cows (Garcia-Winder et al., 1987) and heifers (Anderson et al., 1996). We found that exposure of ovariectomized, nutritionally induced anovulatory cows to progesterone for 7 d increased the amplitude of LH pulses in serum and abundance of messenger RNA for LHß in the pituitary (Looper et al., 2003). Progesterone treatment also increases the number of progesterone receptors in the uterus (Zollers et al., 1993). Increased progesterone receptors in the uterus may control the timing of PGF₂ release and allow normal luteal activity in the subsequent estrous cycle (Cooper et al., 1991).

	Implications

Top Abstract Introduction Materials and Methods Results Discussion Implications Literature Cited

 
Body condition of beef cows at parturition influences the intervals from parturition to first estrus, luteal activity, and conception. Duration of first postpartum luteal activity and the occurrence of estrous behavior associated with first normal luteal activity were not influenced by body condition at parturition or postpartum weight change. Increases in plasma concentrations of progesterone for several days before estrus may enhance subsequent normal luteal function in postpartum beef cows.

	Footnotes

 
¹ Approved for publication by the Director, Oklahoma Agric. Exp. Stn. This research was supported under project H-2331.

² Present address: USDA-ARS, Dale Bumpers Small Farms Research Center, Booneville, AR 72927.

³ Present address: Animal Reproduction and Biotechnology Laboratory, Colorado State University, Fort Collins, CO 80523.

⁴ Correspondence—phone: 405-744-6077; fax: 405-744-7390; E-mail: rpw{at}okstate.edu.

Received for publication January 23, 2003. Accepted for publication May 23, 2003.

	Literature Cited

Top Abstract Introduction Materials and Methods Results Discussion Implications Literature Cited

 


Anderson, L. H., C. M. McDowell, and M. L. Day. 1996. Progestin-induced puberty and secretion of luteinizing hormone in heifers. Biol. Reprod. 54:1025–1031.[Abstract]

Bellows, R. A., and R. E. Short. 1978. Effects of precalving feed level on birth weight, calving difficulty and subsequent fertility. J. Anim. Sci. 46:1522–1528.[Abstract/Free Full Text]

Berardinelli, J. G., R. A. Dailey, R. L. Butcher, and E. K. Inskeep. 1979. Source of progesterone prior to puberty in beef heifers. J. Anim. Sci. 49:1276–1280.

Braden, T. D., M. E. King, K. G. Odde, and G. D. Niswender. 1989. Development of preovulatory follicles expected to form short-lived corpora lutea in beef cows. J. Reprod. Fertil. 85:97–104.[Abstract]

Chamley, W. A., H. A. Jonas, and R. A. Parr. 1976. Content of LH, FSH, and growth hormone in the pituitaries of pregnant and anestrous sheep. Endocrinology 98:1535–1538.[Abstract]

Ciccioli, N. H., and R. P. Wettemann. 2000. Influence of nutrition on estrus and ovarian function of postpartum primiparous beef cows. J. Anim. Sci. 78(Suppl. 2):13 (Abstr.).

Cooper, D. A., D. A. Carver, P. Villeneuve, W. J. Silvia, and E. K. Inskeep. 1991. Effects of progestogen treatment on concentrations of prostaglandins and oxytocin in plasma from the posterior vena cava of post-partum beef cows. J. Reprod. Fertil. 91:411–421.[Abstract]

Copelin, J. P., M. F. Smith, H. A. Garverick, and R. S. Youngquist. 1987. Effect of the uterus on subnormal luteal function in anestrous beef cows. J. Anim. Sci. 64:1506–1511.

Corah, L. R., A. P. Quealy, T. G. Dunn, and C. C. Kaltenbach. 1974. Prepartum and postpartum levels of progesterone and estradiol in beef heifers fed two levels of energy. J. Anim. Sci. 9:380–385.

Dunn, T. G., J. E. Ingalls, D. R. Zimmerman, and J. N. Wiltbank. 1969. Reproductive performance of 2-year-old Hereford and Angus heifers as influenced by pre- and post-calving energy intake. J. Anim. Sci. 29:719–726.

Edqvist, L. E., H. Kindahl, and G. Stabenfeldt. 1978. Release of prostaglandin F₂ during the bovine peripartal period. Prostaglandin. 16:111–119.[Medline]

Garcia-Winder, M., P. E. Lewis, E. C. Townsend, and E. K. Inskeep. 1987. Effects of norgestomet on follicular development in postpartum beef cows. J. Anim. Sci. 64:1099–1109.

Gonzalez-Padilla, E., J. N. Wiltbank, and G. D. Niswender. 1975. Puberty in beef heifers. I. The interrelationship between pituitary, hypothalamic and ovarian hormones. J. Anim. Sci. 40:1091–1104.

Graves, W. E., J. W. Lauderdale, E. R. Hauser, and L. E. Casida. 1968. Relation of postpartum interval to pituitary gonadotropins, ovarian follicular development and fertility in beef cows. Univ. Wisconsin Res. Bull. 270:23–26.

Humphrey, W. D., C. C. Kaltenbach, T. G. Dunn, D. R. Koritnik, and G. D. Niswender. 1983. Characterization of hormonal patterns in the beef cow during postpartum anestrus. J. Anim. Sci. 56:445–453.

Kesler, D. J., T. R. Troxel, and D. L. Hixon. 1980. Effect of days postpartum and exogenous GnRH on reproductive hormone and ovarian changes in postpartum suckled beef cows. Theriogenology 13:287–296.

Lents, C. A., F. J. White, D. L. Lalman, and R. P. Wettemann. 2000. Effects of body condition of beef cows at calving and protein supplementation on estrous behavior and follicle size. Okla. Agric. Exp. Sta. Res. Rep. P-980:164–168. Available: http://www.ansi.okstate.edu/research/2000rr/30.htm. Accessed April 10, 2002.

Looper, M. L., J. A. Vizcarra, R. P. Wettemann, J. R. Malayer, T. D. Braden, R. D. Geisert, and G. L. Morgan. 2003. Influence of estradiol, progesterone, and nutrition on concentrations of gonadotropins and GnRH receptors, and abundance of mRNA for GnRH receptors and gonadotropin subunits in pituitary glands of beef cows. J. Anim. Sci. 81:269–278.[Abstract/Free Full Text]

Moss, G. E., T. E. Adams, G. D. Niswender, and T. M. Nett. 1980. Effects of parturition and suckling on concentrations of pituitary gonadotropins, hypothalamic GnRH and pituitary responsiveness to GnRH in ewes. J. Anim. Sci. 50:496–502.

Odde, K. G., H. S. Ward, G. H. Kiracofe, R. M. McKee, and R. J. Kittok. 1980. Short estrous cycles and associated serum progesterone levels in beef cows. Theriogenology 14:105–112.

Perry, R. C., L. R. Corah, G. H. Kiracofe, J. S. Stevenson, and W. E. Beal. 1991. Endocrine changes and ultrasonography of ovaries in suckled beef cows during resumption of postpartum estrous cycles. J. Anim. Sci. 69:2548–2555.[Abstract]

Pratt, B. R., J. G. Berardinelli, L. P. Stevens, and E. K. Inskeep. 1982. Induced corpora lutea in the postpartum beef cow. I. Comparison of gonadotropin releasing hormone and human chorionic gonadotropin and effects of progestogen and estrogen. J. Anim. Sci. 54:822–829.

Ramirez-Godinez, J. A., G. H. Kiracofe, R. M. McKee, R. R. Schalles, and R. J. Kittock. 1981. Reducing the incidence of short estrous cycles in beef cows with norgestomet. Theriogenology 15:613–623.

Ramirez-Godinez, J. A., G. H. Kiracofe, R. R. Schalles, and G. D. Niswender. 1982. Endocrine patterns in the postpartum beef cow associated with weaning: A comparison of the short and subsequent normal cycles. J. Anim. Sci. 55:153–158.

Rawlings, N. C., L. Weir, B. Todd, J. Manns, and J. H. Hyland. 1980. Some endocrine changes associated with the post-partum period of the suckling beef cow. J. Reprod. Fertil. 60:301–308.[Abstract]

Richards, M. W., J. C. Spitzer, and M. B. Warner. 1986. Effect of varying levels of postpartum nutrition and body condition at calving on subsequent reproductive performance in beef cattle. J. Anim. Sci. 62:300–306.[Abstract/Free Full Text]

Rutter, L. M., T. D. Carruthers, and J. G. Manns. 1985. The postpartum induced corpus luteum: Functional differences from that of cycling cows and the effects of progesterone pretreatment. Biol. Reprod. 33:560–568.[Abstract]

Selk, G. E., R. P. Wettemann, K. S. Lusby, J. W. Oltjen, S. L. Mobley, R. J. Rasby, and J. C. Garmendia. 1988. Relationships among weight change, body condition and reproductive performance of range beef cows. J. Anim. Sci. 66:3153–3159.

Shipka, M. P. 2000. A note on silent ovulation identified by using radiotelemetry for estrous detection. App. Anim. Behav. Sci. 66:153–159.

Spitzer, J. C., D. G. Morrison, R. P. Wettemann, and L. C. Faulkner. 1995. Reproductive responses and calf birth weight and weaning weights as affected by body condition at parturition and postpartum weight gain in primiparous beef cows. J. Anim. Sci. 73:1251–1257.[Abstract]

Vizcarra, J. A., R. P. Wettemann, T. D. Braden, A. M. Turzillo, and T. M. Nett. 1997. Effect of gonadotropin-releasing hormone (GnRH) pulse frequency on serum and pituitary concentrations of luteinizing hormone and follicle-stimulating hormone, GnRH receptors, and messenger ribonucleic acid for gonadotropin subunits in cows. Endocrinology 138:594–601.[Abstract/Free Full Text]

Wagner, J. J., K. S. Lusby, J. W. Oltjen, J. Rakestraw, R. P. Wettemann, and L. E. Walters. 1988. Carcass composition in mature Hereford cows: Estimation and effect on daily metabolizable energy requirement during winter. J. Anim. Sci. 66:603–612.

Werth, L. A., J. C. Whittier, S. M. Azzam, G. H. Deutscher, and J. E. Kinder. 1996. Relationship between circulating progesterone and conception at the first postpartum estrus in young primiparous beef cows. J. Anim. Sci. 74:616–619.[Abstract]

Wettemann, R. P., T. W. Beck, E. J. Turman, and R. L. Hintz. 1982. Endocrine response of postpartum anestrous beef cows to GnRH or PMSG. Theriogenology 18:599–613.

Wettemann, R. P., E. J. Turman, R. D. Wyatt, and R. Totusek. 1978. Influence of suckling intensity on reproductive performance of range cows. J. Anim. Sci. 47:342–346.[Abstract/Free Full Text]

White, F. J., R. P. Wettemann, M. L. Looper, T. M. Prado, and G. L. Morgan. 2002. Seasonal effects on estrous behavior and time of ovulation in nonlactating beef cows. J. Anim. Sci. 80:3053–3059.[Abstract/Free Full Text]

Williams, G. L., and D. E. Ray. 1980. Hormonal and reproductive profiles of early postpartum beef heifers after prolactin suppression or steriod-induced luteal function. J. Anim. Sci. 50:906–918.

Zollers, Jr., W. G., H. A. Garverick, M. F. Smith, R. J. Moffatt, B. E. Salfen, and R. S. Youngquist. 1993. Concentrations of progesterone and oxytocin receptors in endometrium of postpartum cows expected to have a short or normal oestrous cycle. J. Reprod. Fertil. 97:329–337.[Abstract]

This article has been cited by other articles:

				C. A. Lents, F. J. White, N. H. Ciccioli, R. P. Wettemann, L. J. Spicer, and D. L. Lalman Effects of body condition score at parturition and postpartum protein supplementation on estrous behavior and size of the dominant follicle in beef cows J Anim Sci, October 1, 2008; 86(10): 2549 - 2556. [Abstract] [Full Text] [PDF]

				R. Flores, M. L. Looper, R. W. Rorie, M. A. Lamb, S. T. Reiter, D. M. Hallford, D. L. Kreider, and C. F. Rosenkrans Jr. Influence of body condition and bovine somatotropin on estrous behavior, reproductive performance, and concentrations of serum somatotropin and plasma fatty acids in postpartum Brahman-influenced cows J Anim Sci, May 1, 2007; 85(5): 1318 - 1329. [Abstract] [Full Text] [PDF]

This Article Abstract Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Looper, M. L. Articles by Wettemann, R. P. Search for Related Content PubMed PubMed Citation Articles by Looper, M. L. Articles by Wettemann, R. P.