3.1. Body Weight and Body Condition Score Evolution during Two Consecutive Production Cycles
The BW and BCS of ewes at different physiological stages (mating, lambing, and weaning) as well as the variations among them according to breed and year are shown in
Table 1.
As ewes were conducted under similar conditions, ewes of both breeds started mating with similar BWs and BCSs (
Table 1), averaging approximately 45 ± 5.5 kg (
p = 0.1) and 1.89 ± 0.7 (
p = 0.17). They also reached lambing with similar BWs (43 ± 5.1 kg,
p = 0.06) and comparable BCSs averaging 1.71 (
p = 0.57). At weaning, both breeds had similar BW, but a slightly higher BCS (
p = 0.001) occurred for BB ewes compared to QFO ones (1.58 ± 0.63 vs. 1.42 ± 0.54). Between mating and lambing, the BB ewes drew more reserves compared to the QFO ones; however, among lambing and weaning, the QFO group mobilized significantly more reserves than the BB one (
p = 0.001). Among both years, no differences were recorded for BW at mating. However, in the second year, a decline in the BCS was clearly observed (2.01 vs. 1.78), which could be explained by the lack of rain, which did not exceed 250 mm, which consequently affected pasture and the food availability. Hence, ewes lost approximately 12% (
p < 0.05) of their BCS compared to the first year. Atti et al. [
1] and González-García et al. [
16] have observed similar year-dependent effects on the BCS at mating in spring. In addition, at lambing and for both breeds, ewes’ BR loss was approximately 11% of their BCS compared to the first year. These variations explain the higher reserve mobilization in order to face difficult conditions and to cover their conception needs and successfully raise offspring.
The body weight and BCS evolutions are presented in
Figure 3,
Figure 4 and
Figure 5. All curves present similar shapes for all flocks during both years.
The BW and BCS were simultaneously assessed with the aim of an effective description of the dynamics of body reserves in ewes, covering both mobilization and accretion processes [
2,
24]. Regardless of the breed, the BW of all ewes increased during pregnancy in relationship to the anabolism of pregnancy combined with the fetus growth and development [
5,
25]. However, the BCS at both the lumbar and caudal levels recorded a decrease during this stage; this decrease reflects the decrease in the corporal mass of ewes and confirms the better accuracy of the BCS as a tool to assess BR. Then, BW and the BCS decreased between lambing and weaning; this drop indicates the imbalance between energy intake and the animals’ needs given the peak of milk production. A high priority given to the newborn lambs and thus dams could not meet their energy requirements [
26,
27]. Similar results were recorded when ewes mobilized their BR from lambing to weaning to meet the lambs’ requirements, causing low BW and BCSs [
1,
8,
16]. After lambs’ weaning, regardless the breed, ewes’ BW and BCS increased again, given that the ewes became free from their offspring and their nutritional condition was improved [
28]. This confirmed other results that explained the increase in BW and BCS during the post-weaning period due to the decrease in the ewes’ energy requirements [
18,
26] and dietary diversification for lambs. This is consistent with the findings of Kharrat and Bocquier [
29] for goats, who reported that BR replenishment was prioritized at the end of suckling. The BR mobilization continued intensively for all breeds and for both years during the lambing and suckling stages, due to the highest energy needs induced by these physiological stages and accompanied by food scarcity. The BW and BCS profiles recorded in the current study in such conditions are consistent with the previously described dynamics between mating and weaning [
1,
5,
16], showing the use of BR from mid-pregnancy until the end of the suckling period, which is revealed by a decrease in the BCS [
5]. During lactation, irrespective of breed and lambing BCS, all ewes mobilize their BR to produce milk, even for ewes with poor BCS. The same trend as for goats was previously reported for sheep [
29,
30]. The BR mobilization is accentuated by low and restricted feeding, which could explain the decline of BCS at weaning in the second year of the current study, with less rainfall and thus less feed availability, where ewes weaned their lambs with poorer body conditions compared to the first campaign.
The ewes’ BCS frequency varied from one physiological stage to another due to the BR dynamics. At mating, meagre ewes with BCS < 1.5 represented only 19% of the total ewes, which rose to 47% at lambing, while the middle-scored females with BCSs between 1.5 and 2.5 decreased from 67 to 44.8%, and only 8.8% of ewes reached lambing with a BCS higher than 2.5. The dramatic climb in the meagre ewes’ proportion vs. the fall in the proportion of middle- and well-scored ewes shows the degree of underfeeding during pregnancy and the ability of these ewes to cope with great resilience. This phenomenon continued up to weaning, where the proportion of ewes having a BCS < 1.5 continually increased to reach 56% compared to lambing and those with a BCS superior to 2.5 did not exceed 6%. These results clearly show the mobilization of BR during pregnancy, early lambing, and suckling, causing ewes to reach weaning with poor body condition scores but with weaned lambs.
3.2. Reproductive Performances of Ewes
Data on reproductive parameters (fertility and prolificacy) are shown in
Table 2.
In the current study, the fertility rates for both breeds were similar, averaging 75%, which was lower than the previously recorded results [
31]. The low observed fertility rate indicates a potential shift or change in fertility patterns among these breeds, especially with climate variations and feeding resource fluctuations, which are consolidated by the slight decrease of fertility in the second year but without significant differences (
p > 0.05). For both years, prolificacy rates were similar in both breeds and did not exceed 111%, being lower than the average value reported by the National service of Control Performances (119%). This relatively low rate of prolificacy may be in part explained by the lack of rain and the high temperatures during these two campaigns, which highly affected the pasture productivity and grass quality, and thus resulted in poor dietary behavior. In fact, ewes properly fed before and during the mating period will be relatively more prolific than underfed and leaner ewes [
1]. It was reported that under the influence of climate changes or of the quantity and quality of grazed forage, supplementary feeding prior to the mating period could improve reproduction traits such as fertility and prolificacy [
32].
The BW at mating (
Table 2) significantly affected fertility but not the prolificacy rates. The lowest fertility (65%) was attributed to the lighter ewes weighing less than 40 kg. However, a regular fertility rate improvement, with a body weight increase, was observed to reach 80% for ewes weighing more than 50 kg at mating. Similar results were recorded for these breeds or for other breeds, confirming that the fertility rate increases with body weight increases [
33]. Fertility was also highly affected by BCS at mating (
Table 2). Ewes with poor BCS inferior to 1.5 had a significantly lower fertility rate averaging 58%, compared to ewes with a BCS between 1.5 and 2.5 and even for those exceeding 2.5 (75–80%), as previously shown [
34].
Indeed, the positive effects of higher BW and BCSs around mating on the lambing parameters of various sheep breeds have been reported in different production systems [
8,
35]. Thus, the low fertility rate could be the consequence of ewes’ BW or BCS that are too low to respond to the ram effect with the prevention of estrus and fertility [
36].
Ewes having a low BCS have higher prenatal and neonatal mortalities [
37] and a lower survival rate. Similar results were found, suggesting that the poor BCS caused by a decrease in nutrient uptake induces sub-nutrition, diminishing the endometrial sensitivity to progesterone and affecting embryo survival [
32]. Generally, a greater BCS at mating leads to an increased probability to manifest estrus and a higher ovulation rate, and subsequently, to a higher percentage of lambing potential [
32,
34]. Many researchers have reported that fertility is affected by BCS, and higher fertility rates were recorded for females with BCSs between 2 and 4 [
38]. Different results accomplished in different regions on various genotypes were recorded [
34]. The highest prolificacy rate was recorded for ewes whose BCS at mating was superior to 2.5, reaching 115% but without significant differences. However, it was reported that the BCS had a significant effect on litter size [
20,
24].
In this study, the fertility rate was positively correlated with the BW and BCS at mating and the correlations were highly significant (
Table 3).
Indeed, many reports suggested a positive correlation between the BCS and reproductive performance [
8,
34]. The estimation of BR at mating by means of BW or the BCS has demonstrated the existence of a positive relation to ovulation rate and fertility, or to a lesser extent, the prolificacy of several sheep breeds [
1,
26]. However, fertility was negatively correlated with BW and the BCS at lambing but the correlations were low and significant. Likewise, the fertility was correlated with variations in BW (r = 37) and BCS (r = 40) between mating and lambing with highly significant correlations. Prolificacy was positively correlated with BW at mating but negatively correlated with BCS at mating. Prolificacy was negatively correlated with BW and the BCS at lambing and both correlations were low and insignificant. However, the prolificacy was strongly and positively correlated with the variation in the BCS between mating and lambing.
For both fat-tailed Barbarine flocks, the estrus and lambing frequency during both years are shown in
Figure 6.
Before male introduction, all ewes were anovulatory; in the first year, the proportions of ewes that had a normal induced cycle (up to 18 days) were 54 and 62% for B1 and B2, respectively. However, for the second year, these proportions were only 46 and 54% for B1 and B2, respectively. Another estrus wave appeared around the 24th day, and then these ewes displayed a short induced cycle followed by a normal cycle [
39] averaging 27% and 28% for year 1 and year 2, respectively. Beyond the 24th day, for both years, a low proportion of females manifesting estrus behavior was observed; it did not exceed 10 and 5% for year 1 and year 2, respectively. Hence, one month after the rams’ introduction, approximately 98 and 90% of ewes for B1 and B2, respectively, had shown estrus behavior. Then, the rate of return to estrus was low, averaging 7%. However, in the second year, only 79 and 86% of ewes from B1 and B2, respectively, showed estrus behavior, with an average decrease of 10% in comparison to the first year. This result is clearly due to the poorer nutrition and thus lower BCS of ewes in the second year. It was reported that for ewes with low BCSs, the absence or attenuation of estrus can occur, and females with higher BCSs had a higher probability to manifest estrus [
24]. The lambing distribution showed a total of 83 and 82% for B1 and B2, respectively, up to 24 days from the beginning of lambing in the first year. However, in the second year, 83 and 71% of ewes from B1 and B2, respectively, lambed within the first 24 days of lambing.
3.3. Offspring Growth Performances
Lambs’ growth parameters are shown in
Table 4.
Despite the difference among breeds (fat-tailed vs. thin-tailed), they drew similarly upon their reserves to give birth to lambs with the same birth weights (Bi-W) and similar growth parameters. However, in other studies, it has been reported that the breed significantly influenced the post-natal lambs’ growth in relationship with the own genotype effect, which manifests when lambs become independent of maternal effects [
40]. The lambs’ birth weight was significantly lower in the second year (
p < 0.05). The effect of the year and the lambing season, in grazing systems, on the lambs’ birth weight was previously recorded [
41]. Lambs’ post-natal growth depends on the birth weight, the milk production of ewes, and the rate of introduction of solid food into their diet. Given the food shortage in the second year, milk production was presumably affected and consequently the lambs’ growth during all growth periods was also affected, which explains the inferior weights and ADG in the second year. The sex did not affect the lambs’ birth weight, which confirms other results [
42]. However, at 30 and 70 days of age, males were heavier than females and the same tendency was recorded for both ADG. The lambs’ sex’s effect on the birth and advanced weights was previously reported, where male lambs were heavier than females [
16,
40]. The birth type significantly affected birth weight, weights at 30 and 70 days, and both ADG. In fact, single-born lambs were heavier than multiple-born ones (
p < 0.001). This result corroborates other results [
16,
42] suggesting that the birth type significantly affects the birth weight.
The BCS at lambing did not affect lambs’ Bi-W; it was comparable for lambs of both breeds and years, averaging 3.81 kg. Similar results were recorded for the same breed [
28] and other breeds [
42]. However, in others works, the ewes’ BCS did not highly affect the total lamb birth weight and lamb weaning weight [
18]. It is clear that thin ewes have mobilized their BR during pregnancy to respond to the pregnancy needs [
25]. In the current study, ewes with the highest BCS at lambing produced lambs with higher birth weights compared to ewes with low BCSs [
32]. It was suggested that when ewes are malnourished throughout the final phase of pregnancy, negative effects can occur, especially during the postpartum moment, leading to less milk production with further negative consequences on the development of their lambs [
43].
Both weights (W30 and W70) and both ADG were significantly higher for ewes with BCSs at lambing superior to 2; however, ewes with lower BCSs birthed lighter lambs. A positive relationship among ewes’ BCSs and lambs’ growth was reported [
44]. These differences could be the consequence of a higher milk production, due to an intense BR mobilization of ewes both under better body conditions and under undernutrition conditions, causing them to produce more milk to lactate their lambs [
25]. Indeed, some works recorded a significant effect of the BCS at lambing on the lamb birth weight and at the ages of 30, 60, 90, and 120 days [
45]. However, other ones reported no effect [
20,
33,
42]. This variation is probably the consequence of the timing of the BCS measurement, the ewes’ nutrition and specific breeds’ characteristics. It was shown that the BW and BCS of ewes with a maternal ability for lamb growth and/or high genetic merit would drop during suckling, especially at the beginning; the mobilized BR would be used in milk production. Nevertheless, these animals have the capacity to reconstitute new BR during other stages [
8,
28,
35]. All growth parameters were significantly affected by BCS at weaning; the higher values were recorded for lambs issued from ewes with BCSs superior to 1.5. For all lambs, both ADG were almost similar.
Negative and significant correlations (
p < 0.01) were established between the BW and BCS at lambing and the birth weight (
Table 5). Hence, ewes with an ability to mobilize BR during pregnancy reached lambing with low BCSs but gave birth to heavier lambs than those that did not mobilize BR. Both weights at the ages of 30 and 70 days were positively correlated with the changes in the BW and BCS between lambing and weaning, especially for W30. This growth parameter was strongly correlated with BW and BCS variations; the high coefficient of the regression analysis (
Table 6) explains these correlations (0.91 and 0.78 for W30 and W70, respectively).
Both ADG showed a significant negative correlation with BW at weaning; however, they were positively correlated with the variation in BW between lambing and weaning. Additionally, the robustness of this result is emphasized by high regression coefficients (
Table 6) exceeding 0.9 (0.98 and 0.95 for ADG0–30 and ADG30–70, respectively). These results also confirm the behavior of resilient ewes, which continually mobilize their BR to achieve better growth of their offspring than other ewes, reaching weaning in a poor body condition. A moderately positive correlation (r = 0.26) between ADG0–30 and BCS at weaning was recorded, while ADG30–70 was negatively correlated with this parameter and the correlation was highly significant (r = −0.91). However, in earlier results, positive and significant correlations between all growth parameters (BW and ADG) and BW/BCS at lambing were recorded [
25,
44]. The correlations of both daily gains with the BCS variation were not significant (
Table 5). By contrast, strong positive genetic correlations between ewes’ BR (BW or BCS) and lambs’ growth parameters were reported [
4,
5,
35].