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An automated method for the evaluation of ram libido in real mating conditions
- M. Alhamada, N. Debus, F. Bocquier
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We investigated if sexual behaviour of rams can be assessed with an electronic Alpha-Detector (AD) which automatically records mounts of mating rams. To evaluate the rams’ libido (i.e. all sexual activities), we used six intact and six vasectomised rams in pen tests in three different seasons (late spring, autumn and early spring). The pen tests consisted of 30-min visual observations of each ram placed in a group of six Merino ewes (three ewes in oestrus and three ewes not in oestrus). In the pen tests, sexual behaviour was recorded and divided into two categories: pre-copulatory and copulatory. For validation purposes, during the pen tests the 12 rams were equipped with the AD and the number of times the 18 oestrous ewes were mounted were counted over a period of 3 days. Of the 1191 mounts visually identified in the six 30-min sessions, 1026 were recorded automatically by the AD (i.e. 94%). The paddock test is an automated method consisting of the same rams wearing an AD and placed in a flock of ~250 Merino ewes on two occasions (late spring (spring 1) and early spring of the following year (spring 2)), their copulatory activities were automatically recorded over a 5-day period. The results of the pen tests in the three seasons revealed no difference between the two types of rams (breeding v. detecting rams). Based on live observations high correlations (r=+0.81, P<0.003 for breeding and r=+0.76, P<0.02 for detecting rams) were found between pre-copulatory and copulatory behaviours. The libido of the two types of rams measured in pen tests showed high repeatability across the three seasons (83 and 75%, P<0.05 for copulatory and pre-copulatory behaviours, respectively). When measured automatically in paddock tests over two consecutive springs, even higher repeatability was observed in both breeding (94%; P<0.01) and detecting rams (97%; P<0.004) in the number of mounts. In addition, high correlations (+0.89<r<+0.94) between copulatory behaviours, as measured by live observations, and those measured by the AD were obtained. The automatic measurement of ram libido in paddock tests appears to be more reliable than pen tests and far less time consuming. We therefore recommend this automated method to estimate the libido of rams. In addition, this method can be used at any season of the year provided that ewes in oestrus are present in the flock.
New insights into the influence of breed and time of the year on the response of ewes to the ‘ram effect’
- A. Chanvallon, L. Sagot, E. Pottier, N. Debus, D. François, T. Fassier, R. J. Scaramuzzi, C. Fabre-Nys
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Exposure of anoestrous ewes to rams induces an increase in LH secretion, eventually leading to ovulation. This technique therefore is an effective, low-cost and hormone-free way of mating sheep outside the breeding season. However, the use of this technique is limited by the variability of the ewes’ responses. In this study, our objective was to understand more completely the origins of this variability and to determine the relative roles of breed, the point in time during anoestrus and the depth of anoestrus on the response to the ‘ram effect’. In the first experiment, the pattern of anoestrus on the basis of the concentration of progesterone determined weekly, was determined in four breeds including two less seasonal (Mérinos d'Arles and Romane), one highly seasonal (Mouton Vendéen) and one intermediate (Île-de-France) breeds. Anoestrus was longer and deeper in Mouton Vendéen and Île-de-France than in Romane or Mérinos d'Arles. In the second experiment, we used the same four breeds and tested their hypophyseal response to a challenge with a single dose of 75 ng gonadotrophin-releasing hormone (GnRH) in early, mid and late anoestrus, and then we examined their endocrine and ovarian responses to the ‘ram effect’. Most (97%) ewes responded to GnRH and most (93%) showed a short-term increase in LH pulsatility following the ‘ram effect’. The responses in both cases were higher in females that went on to ovulate, suggesting that the magnitude of the hypophyseal response to a GnRH challenge could be a predictor of the response to the ‘ram effect’. As previously observed, the best ovarian response was in Mérinos d'Arles at the end of anoestrus. However, there was no relationship between the proportion of females in the flock showing spontaneous ovulation and the response to the ‘ram effect’ of anoestrous ewes from the same flock.
Expression of seasonality in Merinos d’Arles ewes of different genotypes at the MT1 melatonin receptor gene
- J. Teyssier, M. Migaud, N. Debus, C. Maton, E. Tillard, B. Malpaux, P. Chemineau, L. Bodin
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Spontaneous ovulatory activity (SOA) in spring has been used to study the out-of-season breeding ability of Merinos d’Arles (MA) ewes. Within this breed, an association was found between more intense seasonality and genotype −/− at a MnlI restriction site (allele − for its absence v. + for its presence) in Exon II of the MT1 receptor gene. This study was designed to ascertain whether this association results in a direct effect of the MT1 genotype on the expression of seasonality in MA ewes. In the first year of the study, genotyping of 314 MA ewes at locus MnlI was carried out and resulted in frequencies of 43.0%, 44.9% and 12.1% for genotypes +/+, +/− and −/−, respectively. The SOA of these ewes was determined in early April of two consecutive years by assaying plasma progesterone concentrations in two blood samples taken 9 days apart. Groups of 30 ewes of each homozygous genotype (+/+ and −/−) were identified from this population and their SOA was followed by taking blood samples at regular intervals between January and mid-April of the second and third year of the study. In the second year, groups of ewes were managed together on rangelands, whereas in the third year each group was split into two subgroups given differential feed levels. The results clearly showed that genotype had no significant effect on SOA during the 2- to 3-month period preceding the introduction of rams for spring mating. In the second year of the study, in which the experimental procedure allowed a fair comparison of the fertility of ewes in spring mating, fertility was similar for both genotypes. The reciprocity of the association was not demonstrated and the MnlI polymorphic site could not be used as a genetic marker of selection for out-of-season breeding ability, at least not in the MA breed. The percentage of cycling ewes significantly decreased between January and April, and older ewes (5 or 6 years old depending on the year of the study) were more cyclic than younger ones (2 and 3 years old, respectively). The differential feeding level of ewes from early February did not significantly affect their SOA during the time period studied in the third year of the study.