Technical note
Repeatability and relationship with ®eld mating performance
of a serving capacity pen test in rams
D. Ibarra
a,*, D. Laborde
a, E. van Lier
baDepartment of Animal Reproduction, Faculty of Veterinary Medicine, Universidad de la RepuÂblica,
Lasplaces 1550, Zip Code: 11600 Montevideo, Uruguay
bAnimal and Forage Sciences Department, Faculty of Agriculture, Universidad de la RepuÂblica, Montevideo, Uruguay
Accepted 30 October 1999
Abstract
Two studies were conducted to analyse the repeatability of a serving capacity (SC) pen test and to evaluate the correlation of the results of such a test with ®eld performance. The Laborde SC test, which measures SC by exposing an individual ram for 40 min to two restrained non-oestrous ewes in a pen was used. In the ®rst study, SC was measured on four and six occasions during the autumn of 1994 and 1995, respectively. The results indicated that this test is reliable in measuring SC of rams, since SC was repeatable within, and between, breeding season of consecutive years (p< 0.05). In the second study conducted on two commercial farms, two groups of ewes synchronised with intravaginal sponges containing medroxyprogesterone acetate, were served by rams of high or low SC. On both the farms, the group of ewes served by rams of high SC had higher pregnancy rates than those served by low SC rams (p< 0.05). The Laborde test proved to be a reliable test for the evaluation of SC in rams and that high SC rams had better ®eld performance.#2000 Elsevier Science B.V. All rights reserved.
Keywords:Ram; Serving capacity; Repeatability; Field performance
1. Introduction
The ef®ciency of production in countries in which the sheep industry and particularly meat production is important, depends mainly on the reproductive ef®-ciency of the sheep. In this respect, ram fertility is especially important. Castrillejo (1990) mentioned that 25 % of the rams used for ®eld service are
not clinically ®t for mating. Good management dic-tates that these rams should have their fertility poten-tial evaluated prior to the mating season. Nevertheless, these evaluations seldom include the evaluation of the service capacity (SC) of the rams, which is re¯ected in the scarce literature on the topic. The use of animals with high SC allows reduction of the percentage of males used in ®eld service which also implies a reduction of the related costs (Lindsay, 1986). It has been stated (Kilgour et al., 1985) that SC is a highly heritable trait not only in males but also in females (measured through their behaviour at service). There-*Corresponding author. Tel.:598-2-628-70-67;
fax:598-2-628-01-30.
E-mail address: [email protected] (D. Ibarra)
fore, SC would be a variable to consider in genetic improvement programmes. Lindsay (1986) mentioned the need for progress in the study on service behaviour and the measurement of SC of rams, as an alternative to increase reproductive parameters in sheep. In spite of the numerous ways of measuring libido reported in the literature (Blockey and Wilkins, 1984; Kilgour, 1985; Laborde et al., 1991), and in spite of tests which do not include actual service (Price et al., 1991), no practical test yet exists which has been adopted by the sheep breeders in their routine repro-ductive evaluation.
The aims of the present study were: to analyse the repeatability during the reproductive season and between two consecutive years of an SC test, which could be used under ®eld conditions, and to evaluate the relationship between the results obtained from the SC test and the service performance in the ®eld measured by pregnancy rate.
2. Material and methods
2.1. Study 1
This study was conducted at the Experimental Station No. 1 of the Faculty of Veterinary Medicine, located at 348SL, between March and May 1994 and 1995. Eight adult Corriedale rams with previous sex-ual experience were used. Six of the rams used in 1994 were also used in 1995. All the animals were evaluated clinically for their reproductive ®tness prior to the Laborde SC test. This test measured SC by exposing an individual ram for 40 min to two restrained non-oestrous ewes in a pen. The number of services are counted during the ®rst 20 min and also during the total 40 min. All the animals in the present study were tested on the same day. The tests were repeated four and six times in 1994 and 1995, respectively, with a 1-week interval between the tests. The data were ana-lysed according to Kendall's test of concordance for non-parametric variables.
2.2. Study 2
Two experiments, A and B, were conducted at commercial farms located at 338and 328SL, between March and May 1995. Adult Corriedale rams with
previous sexual experience were used. All the animals were evaluated clinically for their reproductive ®tness prior to the experiment, furthermore, only animals with a scrotal circumference of 30 cm or more were used. One week before the ®eld service, all the rams were tested by the Laborde SC test. According to the results of this test the rams were classi®ed as high SC (4 or more services in 40 min) or low SC (2 or less services in 40 min). These rams were joined with ewes which previously had their oestrus synchronised using intravaginal sponges containing medroxypro-gesterone acetate (SincrovõÂn1, Santa Elena, Monte-video, Uruguay) for 11 days. The experiments were conducted according to a completely randomised block design (Steel and Torrie, 1980). In experiment A, a group of three high and three low SC rams were used together with 122 and 123 ewes, respectively. In experiment B, groups of two high and three low SC rams were used together with 81 and 125 ewes, respectively. In both the experiments, the different groups of rams remained with the ewes in separate ®elds for 4 days; thereafter, the rams were separated from the ewes. Pregnancy diagnosis was performed by transrectal ultrasonography 30 days after service. A statistical package (SAS, 1995) was used to analyse the data using the GLM procedure and applying a model that included the effect of block and of level of SC.
3. Results
3.1. Study 1
The performance of the rams during the tests per-formed in 1994 and 1995 are presented in Table 1and the means in Fig. 1. The results showed that the Laborde test measured SC in the same way in 20 (p< 0.015) as in 40 min (p< 0.008) in each year. The repeatability of the test using data from the six rams tested in both the years showed that in both the years the test measured SC in the same way in 20 min (p< 0.03) and 40 min (p< 0.01).
3.2. Study 2
served by low SC rams were observed (Table 2). In general, the pregnancy rates were high, especially in experiment A, taking into account that the rams only served the ewes during one synchronised heat.
4. Discussion
In order to correctly evaluate the SC of rams, the test used should be highly repeatable, not only within but also between breeding seasons. The results obtained in the ®rst study indicated that the Laborde SC test, applied during the breeding season for Corriedale rams ful®lled these criteria. Kilgour and Wilkins (1980) also mentioned high repeatability for their SC test in which they used oestrous ewes. Kelly et al. (1976), stated that the SC was measured in a similar way when evaluated at various intervals within the breeding season and using different tests. Similar results were reported by Schanbacher and Lunstra (1976), Mickelsen et al. (1982) and D'Occhio and Brooks (1983). It is important to note that young rams in their ®rst breeding season do not display full libido until maturity is reached, implying that the SC test Table 1
Number of services of rams measured by the Laborde test in 20 and 40 min during the autumn of 1994 and 1995
Ram 1994 1995 SCa
time (20±40 min)
1 2 3 4 mean 1 2 3 4 5 6 mean
1 1±2 2±2 3±4 1±1 1.8±2.3 1±3 2±3 0±0 2±2 1±1 1±3 1.2±2.0 M
2 0±0 0±0 1±1 0±0 0.3±0.3 L
3 3±5 3±4 4±6 2±3 3.0±4.5 3±5 3±4 3±5 2±4 4±6 5±6 3.3±5.0 H
4 1±3 4±5 4±6 3±4 3.0±4.5 1±3 3±3 1±3 1±3 1±4 3±5 1.7±3.5 H
5 4±5 2±3 5±7 2±3 2.3±5.0 3±4 3±6 2±4 2±3 2±3 2±3 2.3±3.8 H
6 3±4 2±3 3±4 1±1 2.3±3.0 3±4 2±2 3±6 2±3 2±3 1±2 2.2±3.3 M
7 2±4 0±1 0±0 1±1 0.8±1.5 L
8 2±3 4±5 3±4 4±5 3.3±4.3 3±5 4±6 3±5 5±6 6±9 3±4 4.0±5.8 H
9 0±0 4±6 0±1 0±0 1±3 4±6 1.5±2.7 M
10 4±5 1±2 2±4 3±4 3±5 2±4 2.5±4.0 H
aH: high SC; M: medium SC; L: low SC.
Fig. 1. Mean number of services per ram in 1994 and 1995. Table 2
Pregnancy rates obtained in two ®eld studies (A and B) by using high, and low, service count (SC) rams
High SC ramsa Low SC ramsa
Study A
Rams (n) 3 3
Ewes (n) 122 123
Pregnancy rate (%) 77 a 54 b
Study B
Rams (n) 2 3
Ewes (n) 81 125
Pregnancy rate (%) 57 a 36 b
performed on inexperienced rams may lead to unre-peatable results (Purvis et al., 1984). Price et al. (1991) suggest that prior to testing their SC of virgin ram lambs, they need to gain sexual experience. Barwick et al. (1985) did not ®nd their test to be repeatable when considering only the sexually active rams while also including the inactive rams; the test became repeatable as the inactive rams remained inactive.
Since the Laborde SC test gave similar results when measured for 20 or 40 min, it might be possible to reduce the duration of the test from 40 to 20 min without loosing ef®ciency in detecting rams with high and low SC. A shorter test would be more practical and more easily adopted by the breeders. This is in agreement with the observations of Ibarra et al. (1999) using the same test; nevertheless, other authors dis-agree (Kilgour and Whale, 1980). These authors mentioned that their test did not measure SC in the same way in 60 as in 40 min, when the test was not repeated on the following day.
The results of the second study showed that the pregnancy rate in the ewes served by high SC rams, was higher than for the ewes served by low SC rams. These results are in agreement with those observed by Kilgour (1993) who used a ram/ewe ratio of 0.5/100 at ®eld service, using rams which had previously been evaluated by an SC test designed by the same author. We used three rams per120 ewes which had their oestrus synchronized in a 4-day period, and this is equivalent to a 0.59/100 ram/ewe ratio in a group of ewes having naturally occurring oestrus. Similar results were reported by Mattner et al. (1971), Kelly et al. (1976) and Kilgour and Whale (1980), who found a high correlation between the SC measured in a pen and the ®eld activity (r0.85;r0.45 and
r0.88, respectively). Blockey and Wilkins (1984) and Perkins et al. (1992) also agreed on the high correlation between the results of the SC tests and ®eld performance of the rams and concluded that ewes exposed to high SC rams had a higher lambing rate. Kilgour et al. (1985) observed that rams with a lower SC score, or those which remained inactive during the pen tests, showed a lower service frequency in the ®eld and/or a higher mounts-per-service rate. Barwick et al. (1989), justifying the high correlation between the results of pen tests and ®eld performance, argued that high SC is more important for the overall ¯ock fertility than high scrotal circumference. Furthermore, they
af®rmed that the advantage of the use of high SC rams is more notorious when these rams are used in a high proportion of ewes per ram, as in the present study.
5. Conclusions
Measurement of SC of adult rams with the Laborde SC test is repeatable and is, therefore, a reliable tool to use within, and between, breeding seasons. The use of high SC rams, would make it possible to decrease the percentage of rams used in ®eld service and obtain higher pregnancy rates than when using low SC rams. Laborde test can be used as a practical tool to com-plement the clinical evaluation of reproductive ®tness of rams.
Acknowledgements
The authors wish to thank M. RodrõÂguez and R. Montesdeoca for putting their farms and animals at our disposal for the second study. Thanks also go to J. Piaggio and J. BurguenÄo for their help with the experimental design and the analysis of the data and to A. Lanza and C. VinÄoles for their help with the ®eld work. This study was supported by CSIC and CIDEC (Universidad de la RepuÂblica).
References
Barwick, S., Kilgour, J., Gleeson, A., 1985. Pen test performance and measures of testis diameter. Aust. J. Exp. Agric. 25, 9±16. Barwick, S., Kilgour, J., Fowler, D., Wilkins, J., Harvey, W., 1989. Ram mating performance in Border Leicester and related breed types. 3. Relationships of ram serving capacity, testis diameter, live weight, breed and age with ¯ock fertility, breed and age with ¯ock fertility. Aust. J. Exp. Agric. 29, 17±22.
Blockey, M.A., Wilkins, J., 1984. Field application of the ram serving capacity. In: Lindsay, D., Pearce, D.T. (Ed.), Reproduc-tion in sheep. Aust. Acad. Sci., Camberra, Australia. Castrillejo, A., 1990. Clinical survey of reproductive ®tness in
rams. Veterinaria 26, 15±32 (in Spanish).
D'Occhio, J., Brooks, D., 1983. Seasonal changes in plasma testosterone concentration and mating activity in Border Leicester, Poll Dorset, Rommey and Suffolk rams. Aus. J. Exp. Agric. Anim. Husb. 23, 248±252.
Kelly, R., Allison, A., Shackell, G., 1976. Libido testing and subsequent mating performance in rams. Proc. NZ Soc. Anim. Prod. 35, 204±211.
Kilgour, J., Whale, R., 1980. The relation between mating activity of rams in pens and subsequent ¯ock mating performance. Aust. J. Exp. Agric. Anim. Husb. 20, 5±8.
Kilgour, J., Wilkins, J., 1980. The effect of serving capacity of the ram syndicate on ¯ock fertility. Aust. J. Exp. Agric. Anim. Husb. 20, 662±666.
Kilgour, J., 1985. Mating behaviour of rams in pens. Aust. J. Exp. Agric. 25, 298±305.
Kilgour, J., Barwick, S., Fowler, D., 1985. Comparison of the performance of rams that were sexually active and inactive in pen tests. Aust. J. Exp. Agric. 25, 17±20.
Kilgour, J., 1993. The relationship between ram breeding capacity and ¯ock fertility. Theriogenology 39, 277±284.
Laborde, D., Queirolo, D., PeÂrez, R., LoÂpez, A., Franco, J., 1991. Comparison of three tests of serving capacity in rams 28
Technical meeting of Veterinary Faculty. November, 14-16, Montevideo, Uruguay, pp:57 (in Spanish).
Lindsay, D., 1986. Reproduction in sheep in Australia: a handbook for advisory of®cers. In: Lindsay, D., Kelly, R., Walkley, J.R., Bell, A. (Eds.), Australian Wool Corporation Press, Sidney, Australia.
Mattner, P., Braden, A.W., George, J., 1971. The relation of libido tests to subsequent service activity of young rams. Aust. J. Exp. Agric. Anim. Husb. 11, 473±477.
Mickelsen, W., Pailey, L., Dahmen, J., 1982. Seasonal variations in scrotal circumference, sperm quality, and sexual ability in rams. J. Am. Vet. Med. Assoc. 181 (4), 376±380.
Perkins, A., Fitzgerald, J., Price, E., 1992. Sexual performance of rams in serving capacity tests predicts success in pen breeding. J. Anim. Sci. 70, 2722±2725.
Price, E., Estep, D., Wallach, S.J., Dally, R., 1991. Sexual performance of rams as determined by maturation and sexual experience. J. Anim. Sci. 69, 1047±1052.
Purvis, I., Edey, T., Kilgour, J., Piper, L., 1984. The value of testing young rams for serving capacity. In: Lindsay, D., Pearce, D.T. (Eds.), Reproduction in sheep. Aust. Acad. Sci., Camberra, Australia.
SAS, 1995. SAS/STAT User's guide. SAS Inst., Inc., Cary, NC. Schanbacher, B., Lunstra, D., 1976. Seasonal changes in sexual
activity and serum levels of LH and testosterone in Finnish landrace and Suffolk rams. J. Anim. Sci. 43, 644±650. Steel, R., Torrie, J., 1980. Biostatistics: principles and procedures.
