International Journal of Sheep and Wool Science

International Journal of Sheep and Wool Science Volume 48, Issue 2 2000 Article 2 Effect of ram exposure on out-of-season reproductive performance of young maiden Merino Rambouillet ewes. J Urrutia F Villalpando HCA Meza C Mancilla B Ramirez Copyright c 2000 International Journal of Sheep and Wool Science. All rights reserved.

Urrutia et al. 94 ISSN 0044-78 75/00 Wool Tech. Sheep Breed, 2000, 48 (2), 94-10 1 Effect of Ram Exposure on Out-of-Season Reproductive Performance of Young Maiden Merino Rambouillet Ewes Jorge Urrutia *, Francisco fillalpando 2, Cesar A. Meza H. 3, Carlos Mancilla and Bertha Ram irez Institute Nacional de Investigaciones Forestales, Agricolas y Pecuarias. C.E. Palma de la Cruz, San Luis Potosi, Mexico. Universidad Autonoma de San Luis Potosi, Facultad de Agronomia. San Luis Potosi, Mexico. Unidad Regional Universitaria de Zonas Aridas. Universidad Autonoma Chapingo. A.P.8, Bermejillo, Durango, Mexico. e-mail: cmezacii,,chapin~o.uruza.edu.rnx Sheep Producer * Universidad Autonoma de San Luis Potosi. Facultad de Medicina. San Luis Potosi, Mexico. Summary A trial was conducted to evaluate the ram effect stimulus on the possibility of advancing puberty of ewe lambs as well as on their reproductive performance at two stages of the anestrous season (February to June) in central Mexico (25" 5 1 ' NL). A total of 80 single Merino Rambouillet ewe lambs, 11-13 months-old and 49.0k6.6 kg live weight, were randomly assigned to one of two experimental breeding groups: at the middle (M; March-April) or the end (E; May-June) of the natural anestrous season. Ewes were isolated from rams since they were born and kept under stall-fed conditions. During March and May, ewes were exposed within breeding group to two Merino Rambouillet rams fitted with a marking harness, remaining together for a 45 d-period. To determine ovarian function, blood samples were taken from each ewe to quantify serum progesterone concentrations by RIA. Ewes with less than 0.5 ng ml-' and depicting non-estrual behavior 16 days prior to ram exposure, were classified as inactive. Only 17.5% and 10% (P>0.05) of the M and E groups were defined as reproductively active. From the inactive ewes, 15.1% (M-group) and 77.7% (E-group) (P<0.01), responded to the ram effect, displaying their first estrus 26.6k 4.8 and 22.6k3.8 days after ram exposure (P>0.05), respectively. The observed fertility at first estrus in the M and E groups was 78.5 and loo%, respectively. After 32 days following ram exposure, another 17 and 5 ewes in the M and E groups displayed estrous behavior and had 64.7 and 100% fertility rates e0.05), respectively. Results of this study confii the possibility of advancing puberty in Merino Rarnbouillet ewes by means of the ram effect. This

95 Effect of ram exposure on out-of-season reproductive performance Urrutia, J; et al. 95 practice generated up to 100% fertility rate, 92.5% lambing rate, and 1.16 lambs per lambed ewe that has reached 49.0k6.6 kg live weight, proportionately 0.6 to 0.7 of their mature body weight. Ewes bred at the end of the anestrous season (May-June) had a higher response to the ram effect stimulus and a better reproductive performance than March-bred ewes. Improving the reproductive performance of earlier breeding schemes of young ewes by means of the ram effect could be of economic significance. Keywords: Sheep, ram effect, maiden ewes, anestrous, reproductive efficiency Introduction In Mexico, sheep production faces a similar situation observed in other latitudes: a decreased reproductive activity in ewes as photoperiod increases (Dyrmundsson, 1973; De Lucas, 1987; Lynch et al., 1992). According to Martinez et al. (1999), the anestrous season of Merino Rambouillet ewes in central Mexico (19" 17' NL, 99" 31' WL) started early in February and finished late in June. In fact, while Merino Rambouillet ewes display estrual activity until July or August continuing until January (Urmtia, 1991), an even greater anestrous season is observed in maiden ewes (Dyrmundson, 1973). In Mexico, preliminary studies have shown fertility rates of 70% in 18-month old ewes bred during April and May (Martinez et al., 1989), and 85% fertility rate in young ewes (14-month old) bred either at the middle or the end of the breeding season (Urmtia et al., 1993). Previous studies demonstrated that ewe lambs born during November started ovarian activity after a period of seven months (Urrutia et al., 1994). In addition, when 10- months old ewes were bred, either at the middle or the end of the breeding season, fertility rates of 50% and 2 1% were observed (Urmtia, 1995). Therefore, these findings suggested the possibility to mate Merino Rambouillet ewes prior to an age of 12 to 13- months. However, as mentioned by Land (1972), the anestrous season may constitute an obstacle to schedule more continuous breeding events. The pioneer studies of Schinkel(1954a,b) demonstrated that the sudden presence of active rams during the transition period from the anestrous season to the breeding season, stimulated re-establishment of reproductive activity in ewes. In fact, ewes can be stimulated by the unaccustomed presence of rams to initiate GnRH secretion, and thus increases of tonic secretions of LH are observed. This usually results in ovulation three days after ram introduction (Lynch et al., 1994). The ram effect has been confirmed, among others, by Lishman and Lange (1979), Oldham et al., (1979), Nugent et al., (1988), and Kassem et al., (1989). Later, the ram effect was also demonstrated within the anestrous season (Minton, 1987; Ochoa et al., 1993), and especially in those breeds with longer breeding seasons (Murtagh et al., 1984; Ochoa and Urmtia, 1995).

Urrutia et al. 96 Ram Exposure on Out-of-Season Maiden Merino Ewes 96 While Murtagh et al. (1984) reported a more defined ram effect on younger than adult ewes, Oldham et al. (1985) found a similar response for both classes of age. Recently, Urmtia et al. (1997) reported a similar response in both adult and 16-month old Rambouillet ewes. The aim of this study was to evaluate the practical possibility of the use of the ram effect stimuli on the reproductive performance of maiden 1 1-months old Merino Rambouillet ewes at the middle (March) and ending (May) of the anestrous season under Mexican conditions. Materials and Methods Location, animals and treatments. The study was conducted at the Sheep Unit of the Santa Barbara Ranch, Soledad de Graciano County, San Luis Potosi, Mexico, located at 22" 5 1 ' North Latitude. A total of 80 single maiden Merino Rambouillet ewes born in May of the previous year were randomly assigned to one of two experimental breeding groups within the natural anestrous season for this breed in Central Mexico (February to June): 1). Season I, from March 15 to April 30, for ewes 11 months-old and 49.2k6.5 kg live weight, and 2). Season 11, from May 2 to June 16, for ewes 13 months-old and 49.0A6.6 kg live weight. Ewes were isolated from rams since birth and kept under stallfed conditions. Blood sampling andprogesterone quantzpcation. To verify the reproductive status of each ewe lamb, blood samples were collected via jugular venipuncture into 10 rnl sterile vacutainer tubes (Corvac, Shenvood Medical, St. Louis, MO). Blood was allowed to clot for 30 min at room temperature and serum was harvested after centrifugation (1,500 x g, 15 min, 4 C) and stored at -20 C. Samples were assayed, for progesterone (P,) to determine the functional status of the ovary. Serum P, concentrations were determined by RIA (Diagnostic Products, Los Angeles, CA) at the Cellular Biology Laboratory, College of Medicine, San Luis Potosi Autonomous University. The assay was modified and validated for use in ruminant serum (Schneider and Hallford, 1996). Intra- and inter-assay CV were 7 and 8 %, respectively. Reproductive management. Two 4-years old Merino Rambouillet rams of proven libido and fertility, fitted with a marking harness, were joined with the experimental breeding group at March 15 and May 2. Rams remained for a 45-day period within experimental groups and ewes were checked daily for crayon marks at 0700 and 1900. Wool techno log^ and Sheep Breeding, Vol48 2000

97 Effect of ram exposure on out-of-season reproductive performance Urrutia, J. et al. 97 Criteria to evaluate the Ram effect response. Active ewes: Defined as those ewes having serum P, concentrations greater than 0.5 ng rnl1 and displaying estrus behavior 16 days after ram exposure, were considered as non-elective ewes to evaluate the ram effect response. Inactive-ewes: Defined as those ewes having serum P, concentrations less than 0.5 ng rnl-' at the beginning of both experimental breeding dates and not displaying estrus behavior 16 days after ram exposure, were considered as elective ewes to evaluate the ram effect. From these eligible ewes, the experimental breeding groups were established. Ewes presenting estrous behavior between day 16 to 3 1 after male exposure were considered as positively affected by the ram effect (responsive ewes). On the contrary, those ewes with no signs of estrous 3 1 days after introduction of the rams were classified as negative or non-affected by the ram effect (non-responsive ewes) (Cushwa et al., 1992). Differences between experimental groups with respect to the number of ewes presenting estrus, number of days occurred fiom ram introduction to first estrus, fertility rate (percentage ewe lambed per ewes showing estrus), lambing rate (percentage ewes lambed per ewes joined), were analyzed by chi square test. Continuous variables were evaluated by analyses of variance (Snedecor and Cochran, 1967). All analyses were computed using the SAS System for Linear Models (Littell et al., 1991). Results The number of ewes per experimental group, initial live weight, as well as the percentages of anestrous ewes and responsive ewes, are presented in Table 1. At the beginning of the experimental breeding, active ewes from both the middle (M) and end (E) stages of the anestrous season displayed similar (P>0.05) percentages of ovarian activity, 17.5 and 10.5 %, respectively. Among the anestrous ewes (Table I), the E- group showed the highest response (P<O.O l) to the ram effect (77.7 vs 15.1 %). There was no difference (P>0.05) between the M and E groups with respect to the interval of days between ram exposure and appearance of first estrous, 26.4k4.8 and 22.6k3.8 days respectively. Table 1 Effect of ram exposure on out-of-season reproductive performance of Merino Rambouillet lamb ewes at the middle (March to April) and the end (May to June) of the anestrous season in Central Mexico (25'51' NL) Variables March May Probability Ewe number 40 40 Initial live weight(kg) 49.235.5 49.M6.6 n.s. Anestrous ewes 33 (82.5%) 36 (90.0%) n.s. Responsive ewes 5/33 (15.1%) 28/36 (77.7%) 0.001

Urrutia et al. 98 Ram Exposure on Out-of-Season Maiden Merino Ewes 98 From the initially anestrous ewes that did not present estrus signals during the ftrst 3 1 days after ram exposure, 57.1% (16128) of the M-group and 62.5% (518) of the E- group displayed estrus behavior (P>0.05) between 32 to 42 days after ram introduction. The fertility rate of these late cycling ewes was 62.5% and 100.0%, for the M and E groups (P>0.O5), respectively. In a second analysis (Table 2), all ewes were included to evaluate the out-of-season reproductive performance. While 70% of the M-ewes depicted estrus behavior within the 45 days after ram exposure, 92.5% ofthe E-ewes displayed that behavior (RO.0 I), and fertility rates were 78.6% and 100% (P<0.01), respectively. Lambing rates of these groups were 55.0% and 92.5%, and litter size were 1.23 and 1.16 lambs born per ewe lambed (P>0.05), respectively. Table 2 Out-of-season reproductive performance of Merino Rambouillet ewes lambs at the middle (March to April) and the end (May to June) of the anestrous season in Central Mexico (25'51' NL) 1 Variables March May Probability Ewe number 40 40 Cycling ewes (%) (28140) 70.0 (37140) 92.5 0.01 Fertility rate (%) (22/28) 78.6 (37137) 100.0 0.01 Lambing rate (%) (22140) 55.0 (37/40) 92.5 0.001 Prolificacy (litter size) (27122) 1.23 (43137) 1.16 n.s. Productivity rate (%) (27140) 67.5 (43140) 107.5 0.01 ' Fertility rate, expressed as the number of (lambed ewes per ewes with estrus) 100 Lambing rate, expressed as the number of (lambed ewes per ewe exposed) 100 Productivity rate, expressed as the number of (lambs born per ewe exposed) 100 Discussion In both breeding groups some ewes displayed either estrus behavior within 15-days after ram exposure or had serum progesterone concentrations greater than 0.5 ng ml1. This confirms preliminary studies indicating that maiden Merino Rarnbouillet ewes during the spring months are not totally reproductively inactive under Mexican conditions (De Lucas, 1991). The reduced response of the M-ewes to the ram effect suggests an anestrous season effect. However, since many ofthe M-ewes displayed estrual activity just at the middle of the evaluating period, with 62.5% fertility rate, the anestrous season was not the only variable affecting this low response to the ram stimulus. In fact, because those ewes bred at the end ofthe anestrous season (E-group) were two months older but with similar live weight than those bred as M-group, there may be a breeding season by age interaction between groups. Previous studies have shown that Merino Rambouillet ewes, under similar conditions, display the first estrus or puberty, at 7 to 10 months old (Umtia et al., 1994). However, those bred at 10 months old displayed a lower fertility rate (Urmtia et al., 1995). This

99 Effect of ram exposure on out-of-season reproductive performance Urrutia, J, et al. 99 lower fertility suggests that the onset of oestrus does not necessarily imply full reproductive performance, as it can take from two to four months to reach reproductive maturity. This is supported by the observation that ewes displaying non-estrual behavior within the first 30 days after ram exposure showed estrual activity two months later (at 12 months old). The last even though they were just at the middle of the anestrous season, when the ram effect stimulus was probably diminished. The out-of-season reproductive performance of the E-ewes could be considered as acceptable. This is particularly true when considering that in Mexico, once Merino Rambouillet ewes have had reproductive activity followed by an anestrous season, they re-establish reproductive activity until July oraugust (Urrutia, 199 1). According to Martinez et al. (1989), in 18-month old ewes bred at 17-d intervals, fertility rate declined from 21% in January to 5% in March, then increased (88%) in May. This is consistent with the lower reproductive performance observed in the M-ewes when compared to that observed in the E-ewes. Since there was no difference (P>0.05) in live weight between experimental breeding groups (49.01t6.6 kg), the greater reproductive efficiency observed in the E-group was likely due to the greater reproductive maturity as well as the declining negative photoperiod effect towards the end of the anestrous season. Results of this study confirms the possibility to get up to 100% fertility rate, 92.5% lambing rate, and 1.16 lambs per lambed Merino Rambouillet ewes that have reached 49.0k6.6 kg live weight, proportionately 0.6 to 0.7 of their mature body weight. In fact, ewes bred at the end of the anestrous season (May) had a higher response to the ram effect stimulus as well as a better reproductive performance than March-bred ewes. Improving reproductive performance through breeding young ewes by means of the ram effect could be of economic significance. Acknowledgements The authors wish to acknowledge Ing. JoseAngel Morales, Doiia Barbara Ranch, San Luis Potosi, for providing facilities to develop this research. References Cushwa, W.T., Bradford, G.E., Stabenfeldt, GH., Berger,Y.M., and Dally, M.R. (1992) Ram influence on ovarian and sexual activity in anestrous ewes: effects of isolation of ewes from rams before joining and date of rams introduction. J. Anim. Sci. 70,1195-1200. De Lucas. (1987) Reproductive seasonality in five sheep breeds. M.Sc. Thesis. Universidad Nacional Autonoma de Mexico. Mexico. 95 p. De Lucas, T.J., and Garcia, A.A. (1991) Ovarian activity from March to June in Rambouillet ewes. Proc. N National Congress on Sheep Production. San Cristobal de las Casas, Chiapas, Mexico. p. 136. Wool techno log^ and Sheep Breeding, Vol48 2000

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