RELATIONSHIP OF SEMEN QUALITY AND FERTILITY IN THE RAM TO FECUNDITY IN THE EWE C. V. HULET, WARREN C. FOOTE and R. L. BLACKWELL U.S. Department of Agriculture, Agriculture Research Service, Animal Husbandry Research Division, Dubois, Idaho, and Animal Husbandry Department, Utah State University, Logan, Utah, U.S.A. {Received st August 964) Summary. In 96 the U.S. Sheep Experiment Station flock was used to test the relationship of semen quality and fertility (percentage of ewes lambing) in the ram to fecundity (percentage of lambs born of ewes lambing) in the ewe. The rams were unselected for semen quality and fertility. Six semen traits were significantly correlated with ewe fecundity. The multiple correlation of these six semen traits with fecundity was \m=.\49. The within age group correlation between fertility and fecundity \m=.\3(p<\m=.\). was The correlation was highest in the mature ewes (\m=.\3, P<\m=.\). This study suggests that fecundity in addition to fertility may be affected by the ram. INTRODUCTION It has been shown by Hulet & Ercanbrack (96) that a relationship exists between semen quality and percentage of ewes lambing. Inasmuch as the percentage of ewes successfully impregnated is associated with semen quality it appears logical that in populations in which multiple ovulations are common that the percentage of eggs fertilized and consequently lambs born to those ewes would also be affected by semen quality. We know of no experimental evidence to support or refute this hypothesis. The purpose of this study was to determine the relationship between the semen quality of rams and the fecundity of their mates, and the relationship between fertility and fecundity of groups of ewes to which different rams were mated. MATERIALS AND METHODS In 96, 36 rams (sixty-seven Rambouillet, forty-five Targhee and twentyfour Columbia) used in the regular breeding programme at the U.S. Sheep Ex periment Station were semen tested and individually pen mated, irrespective of semen quality, to from five to sixty-five ewes each during a 34-day, late-autumn breeding period. (Therefore, these rams were unselected for fertility.) Semen samples, recovered from the vaginae of tester ewes as described by Hulet & 3
3 C. V. Hulet et al. Ercanbrack (96), were obtained from only ninety-four of the rams. Therefore, only these rams and their mates were included in that portion of the study investigating the correlation between semen quality and fecundity. The following data were obtained from each semen sample : ( ) Volume. () Motility score (a score of is best, 6 is poorest as described by Hulet & Ercanbrack, 96). (3) % motility (estimated in undiluted sample) (4) ph (ph paper, range 6- to 8-) (5) Concentration (Klett-Sommerson colorimeter estimate, Emik & Sidwell, 947b). (6) Total sperm per ejaculate. (7) % live normal spermatozoa (all morphology observations made from opal blue Breslau and eosin stained smears, Emik & Sidwell, 947a). (8) % abnormal spermatozoa. (9) % abnormal heads. () % abnormal necks (include tailless heads). () % abnormal middlepieces. () % abnormal tails. Ram fertility was defined as the percentage of ewes lambing (of ewes in the flock at lambing time). Fecundity was defined as the percentage of lambs born of ewes that lambed in each mating group. All possible correlations were cal culated among the twelve semen traits of each ram and the fecundity of his mates. The multiple correlation coefficient between semen quality and fecundity was obtained from a multiple regression analysis which included those semen traits which were found to be significantly correlated with fecundity. The entire breeding group of 36 rams was used to study the correlation between ram fertility and ewe fecundity. This correlation was calculated within age group of ewes (, 3 and 4 years of age and older) in order to avoid any founding con of age and lambing rate. A total of 67 ewes was used in this study including 6 -years old, 497 3-years old and 553 4-years old and older. These were nearly equally distributed among the Rambouillet, Targhee and Columbia breeds. Hulet (unpublished data) found small and non-significant effects of breed of ewe and inbreeding coefficient on ovulation rate in 3 Rambouillet, Targhee and Columbia ewes. Therefore these variables were disregarded in this study. RESULTS of ewes with means and variances for the semen traits studied are shown in Table. Both motility score and percentage motility were significantly correlated with traits were also The correlations between the various semen traits and fecundity = fecundity (r -5 and -, P<5). Four morphological significantly correlated with fecundity (P<). They include percentage live normal cells (-33), percentage abnormal cells (-4), percentage abnormal necks ( -4) and percentage abnormal middlepieces ( -44). The incidence
Semen quality and fertility 33 of abnormal middlepieces was much less frequent than the other morphological traits. The multiple correlation, calculated from those traits which were significantly correlated with fertility, was.49 (P<). The distribution of fertility and fecundity according to certain semen quality classifications for four semen traits is shown in Table. The correlation between ram fertility and the fecundity of his mates, cal culated within age groups of the ewes, was -3 and highly significant. The correlation was highest in the mature age group (-3) in which ovulation rate also is known to be highest (Hulet, unpublished data). Table means and variances of semen traits of rams and the relationships between these traits and ewe fecundity (n = 94) PH Motility scoret Motility (%) Volume (ml) Concentration ( 9/ml) Total sperm ( X 9) Live normal (%) Abnormal (%) Abnormal heads (%) Abnormal necks (%) Abnormal middlepieces (%) Abnormal tails (%) Multiple Mean 6-56 - 76-38 -89-89 -8 76-9 5-43 -8 3-4 -53 - Variance -83-8 9-68 -44-8 -8-58 87 3-66 - -75 - Correlation coefficient --8 --5* -* -5-4 -4-33** --4** --6 --4** --44** --4 correlation -49" b' -- -5 --4 --6 --7 --7 Standard partial regressions (b') and multiple correlation were calculated for only those semen traits which were significantly correlated with fecundity. t A score of is best, 6 is poorest as described by Hulet & Ercanbrack * (96). Significant at the -5 level; ** Significant at the - level. DISCUSSION It would be expected that a ewe producing two ova would be more likely to lamb, as well as have a multiple birth, than would a ewe producing only one ovum. Terrill (936), McKenzie & Terrill (937) and Hulet (unpublished data) have shown that ovulation rate is higher in mature than young ewes. Because of a disproportion in the ages of ewes mated to the different rams the fertilityfecundity data were analysed within age groups. Erroneous conclusions could be made if age were disregarded. In this study, ram differences are partially confounded with line differences and, as a result, many rams were related to their mates. Thus, the correlations between ram fertility and ewe fecundity might be due in part to possible genetic correlation between the two traits. However, previous studies including Desai & Winters (95), Ercanbrack (95), Johansson & Hansson (943), Rendei (956) and Sidwell (956) indicate that hereditary factors do not greatly influence fertility or fecundity in sheep. The simple and multiple corre lations between semen quality and fecundity indicate that the correlation between ram fertility and ewe fecundity may be attributed primarily to the
34 C. V. Hulet et al. physiological fertilizing capacity of the ram's sperm cells. This suggests that the fertilization of one ovum in the reproductive tract of ewes producing two ova is partly independent of the fertilization of the other ovum, and that the relative frequency with which both ova are fertilized is correlated with the percentage of ewes that have at least one ovum fertilized. One should not overlook the possibility that the rams might have varied in their contribution to embryo mortality which could contribute to the fertility-fecundity correlation. Again, however, in view of the correlation between semen quality and fecundity and the paucity of evidence that embryo mortality is associated with the semen traits observed in this study, one might conclude that embryo was mortality not an important contributing factor. Table distribution of fertility and fecundity according to semen quality classification No. rams No. ewes Fertility* Fecundity\ Lambing\ Live, normal spermatozoa 8% and above 6 to 79% 4 to 59% to 39% to 9% 6 7 4 4 533 53 7 69 37 3 4 6 83 Abnormal spermatozoa to 9% to 39% 4 to 59% 6 to 79% 8% and above 86 3 786 44 56 6 93 85 5 35 7 43 4 8 5 Abnormal necks to 9% to 39% 4 to 59% 6 to 79% 8% and above 8 54 35 8 9 8 64 35 5 4 3 5 5 64 Motility 8% 6 to 79% 4 to 59% to 39% to 9% and above 37 4 4 7 883 85 9 88 84 36 7 6 8 6 * % ewes lambing of ewes in the flock at lambing time. t % lambs born of ewes lambing. % % lambs born of ewes in the flock at lambing time. Includes tailless heads. The results of this study, in addition to the generally recognized fertility on the earliness and uniformity of the lamb crop, emphasize portance of fertility in the ram. The significance of semen testing improving lamb production is strengthened. effect of ram the im as a tool in
Semen quality and fertility 35 ACKNOWLEDGMENTS This paper is published with the approval of the Director of the Idaho Agri cultural Experiment Station, Moscow, as Research Paper No. 6 and with the approval of the Utah Agricultural Experiment Station, Logan, as Journal Paper No. 47. REFERENCES Desai, R. M. & Winters, L. M. (95) The inheritance offertility in sheep. Indian J. vet. Sci., 9. Emik, L. O. & Sidwell, G. M. (947a) Refining methods of using opal blue stain in evaluating ram semen. J. Anim. Sci. 6, 67. Emik, L. O. & Sidwell, G. M. (947b) Factors affecting the estimation of concentration of sperm in ram's semen by the photoelectrometric method. J. Anim. Sci. 6, 467. Ercanbrack, S. K. (95) Selection indexesfor range Rambouillet, Columbia, and Targhee lambs. Ph.D. thesis, Ames, Iowa. Hulet, C. V. & Ercanbrack, S. K. (96) A fertility index for rams. J. Anim. Sci., 489. Johansson, I. & Hansson, A. (943) The sex ratio and multiple births in sheep. LantbrHôgsk. Annlr,, 45. McKenzie, F. F. & Terrill, C. E. (937) Estrus, ovulation and related phenomena in the ewe. Res. Bull. Mo. agrie. Exp. Sta. 64, 88. Rendel, J. (956) Heritability of multiple birth in sheep. J. Anim. Sci. 5, 93. Sidwell, G. M. (956) Some aspects of twin versus single lambs of Navajo and Navajo crossbred ewes. J. Anim. Sci. 5,. Terrill, C. E. (936) Estrus and ovulation in the ewe, a preliminary report. Proc. Amer. Soc. Anim. Prod., 8th Ann. Meet., p. 53.