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Effect of time of weaning on the reproductive performance of Barbados Blackbelly ewes and lamb growth reared in the tropics
Small Ruminant Research 103 (2012) 205–210
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Effect of time of weaning on the reproductive performance of Barbados Blackbelly ewes and lamb growth reared in the tropics M. Knights a,∗ , N. Siew a,1 , R. Ramgattie a,1 , D. Singh-Knights b,2 , G. Bourne c a b c
University of the West Indies, Department of Food Production, St. Augustine, Trinidad and Tobago University of the West Indies, Department of Agriculture Economics and Extension, St. Augustine, Trinidad and Tobago University of the West Indies, School of Veterinary Medicine, Mount Hope, Trinidad and Tobago
a r t i c l e
i n f o
Article history: Received 19 April 2011 Received in revised form 9 September 2011 Accepted 16 September 2011 Available online 10 October 2011 Keywords: Weaning Sheep Reproduction Average daily gain
a b s t r a c t The effects of time of weaning on subsequent reproductive performance of ewes and the growth of lambs were evaluated in Barbados Blackbelly hair sheep, under a tropical photoperiod. Two experiments were conducted to assess the effect of time of weaning on subsequent reproductive performance of the ewe. In Experiment 1, lactating ewes (n = 56) were weaned early (WE1; 72.6 ± 1.3 days postpartum; n = 31), 21 days prior to introduction to the rams (RI) – or not weaned prior to the breeding period, but temporarily removed from their lambs (n = 25) for 3 days – beginning at ram introduction and then weaned 24 days later (TSE1; 121.2 ± 1.3 days postpartum). In Experiment 2, ewes were either separated from their lambs (n = 29), 17 days prior to ram introduction (RI; WE2; 75.7 ± 1.2 days postpartum) remained with their lambs during the entire breeding period (UW; n = 16), or their lambs temporarily removed for 3 days – beginning at ram introduction (RI) and then re-joined with their dams (n = 13; TSE2). The proportion of ewes lambing, interval from RI to lambing, lambing day during lambing period and prolificacy were not affected by treatment. The lambing interval recorded was longer in late weaned ewes in Experiment 1, but time of weaning had no effect in Experiment 2. To assess the effect of time of weaning on lamb growth, two experiments were conducted in which lambs were weaned either early (EW; 76 or 108 days of age for Experiments 1 and 2, respectively) or late (LW; 186 and 159 days of age for Experiments 1 and 2, respectively). Lambs were weighed at birth, at weaning and at monthly intervals until 1 month following the separation of the late weaned animals from their dams. The effect of time of weaning on ADG showed a significant quadratic period × treatment interaction (P < 0.001). The ADG of the EW-lambs declined after weaning for approximately 2 months, followed by an increase in ADG. In contrast the ADG in the LW-lambs did not change significantly or declined slowly prior to weaning, but showed a sharp decline following weaning. The overall ADG and total live weight gain tended to be or was higher (P < 0.01) in compared to the EW lambs of Experiments 1 and 2, respectively – despite the recovery in ADG in EW-lambs and the decline in ADG, following weaning in LW-lambs. A significant period × treatment interaction (P < 0.001) regarding live weight was recorded, with the difference in live weights being greatest immediately prior to weaning in the LW-lambs. The mortality rate of the lambs was significantly higher (P < 0.01) in the EW- compared to LW-lambs, in Experiment 1 only. Weaning lambs prior to or after
∗ Corresponding author. Current address: Division of Animal and Nutritional Sciences, West Virginia University, PO Box 6108, Morgantown, WV 26506-6108, United States. Tel.: +1 304 293 1946; fax: +1 304 293 2232. E-mail address: [email protected] (M. Knights). 1 Current address: BioSciences Agriculture and Food Technologies (BAFT), University of Trinidad and Tobago, Eastern Caribbean Institute of Agriculture and Forestry (ECIAF) Campus, Centeno, Trinidad and Tobago. 2 Current address: Division of Natural Resources and Design, West Virginia University, PO Box 6108, Morgantown, WV 26506-6108, United States. 0921-4488/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.smallrumres.2011.09.042
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the breeding period did not improve the subsequent reproductive performance of dams, but increased the mortality rate of lambs in some cases, and resulted in an accelerated decline in growth rates, regardless of the age of weaning in hair sheep reared under a tropical photoperiod. Management systems in which the ewes are re-bred 2.5–3.5 months after lambing, and lambs are reared with the ewes until market at 6.5–7.5 months of age provide an opportunity to maximize productivity of ewes, in relation to kg lamb marketed annually. © 2011 Elsevier B.V. All rights reserved.
1. Introduction Productivity of the ewe can be improved by increasing the frequency of lambing. However, the suppressive effect of lactation, superimposed on inhibitory photoperiod, limits the productivity of most ewes in the temperate regions, to one lambing season per year. Attempts to accelerate the frequency of lambing have traditionally relied on highinput management systems that may involve the early weaning of lambs, with or without the use of hormonebased estrous induction therapies (Wheaton et al., 1992; Lewis et al., 1996; Rodríguez et al., 1998). These approaches have yielded moderate or little improvement in ewe productivity, as measured by the frequency of lambing and kg lamb weaned per year (Nugent and Jenkins, 1991). Additionally, early weaning systems increased post weaning lamb management costs, associated with rearing lighter feeder/nursery lambs (Jenkins, 1986), lower post weaning weights (Rastogi, 2001; Wildeus et al., 2005; DeNicolo et al., 2006) and increased post-weaning lamb mortalities (Hatcher et al., 2010). Postpartum uterine involution in sheep is completed by days 30–40 after lambing (O’Shea and Wright, 1984; Hauser and Bostedt, 2002; Gray et al., 2003). The first postpartum estrus being detected by day 32 in a large proportion of suckled and non-suckled ewes lambing during the stimulatory photoperiod of autumn (Lewis and Bolt, 1983). Conception rates did not differ between dry and lactating ewes, but increased as the postpartum interval increased from 30 to 50 days (Warren et al., 1989). These results indicate that, in the absence of an inhibitory long photoperiod, fertile breeding and the establishment of pregnancy can occur in the ewe as early as day 40 postpartum, without the necessity for weaning. Tropical hair sheep breeds have shown a reduced sensitivity to the inhibitory effects of long day photoperiod under temperate environments and generally, breed year round under the relatively constant photoperiod of the tropical conditions (Rastogi, 2001). Therefore, under tropical conditions without the inhibitory effects of season, ewes of the hair sheep breeds may be able to rebreed following a short postpartum period, while suckling their young. However, the effects of extended suckling periods on the reproductive performance of the ewe and growth rates of their lambs have not been fully studied in the tropics. Therefore, the objectives of this study were to determine the effect of lactation/suckling during the breeding period and early pregnancy on the reproductive performance of the Barbados Blackbelly (BBB) ewe, and to determine the effect on live weights and growth rates of their lambs up to marketing or slaughter weight.
2. Materials and methods 2.1. Animals and general management The animals used in this study were of at least 7/8 BBB cross-breds. Ewes were reared in barns on raised slatted floors at the University of the West Indies Field Station, located in Mount Hope, Trinidad and Tobago (10◦ 40 N, 61◦ 31 W). All animals were fed a diet of green forage ad libitum and supplemented with an 18% crude protein concentrate. Lambs were offered the concentrate ad libitum as a creep feed, prior to weaning, with free access following weaning. Following weaning lambs were maintained in barns with a spacing allowance of no less than 0.4 m2 per lamb and in groups of no more than 16. Rams were reared in a separate building prior to their introduction to the females. Breeding periods of 35 and 50 days were used in Experiments 1 and 2, respectively. Prior to introduction of the rams, all ewes were subjected to an estrous synchronization protocol, consisting of injections of progesterone (200 mg dissolved in corn oil, i.m., Sigma–Aldrich) on day −5 (d −5) and day −2.5 (d −2.5). This was followed by prostaglandin F2␣ injections (PGF2␣ , 2× 10 mg 3 h apart, i.m. Lutalyse® Pharmacia and UpJohn, NY) (Hawk and Cooper, 1977), on the day of ram introduction (d0). Rams were joined with ewes in all treatment groups on the same day (d0) at ewe to ram ratios of between 12:1 and 15:1. All rams used in the study were mature and fertility proven. However a breeding soundness examination had not been conducted prior to the experiment.
2.2. Effect of weaning on reproductive performance Two experiments were conducted to determine the effect of time of weaning relative to the breeding period on the reproductive performance of the ewes. In Experiment 1, lactating ewes (n = 56; 72.6 ± 1.3 days postpartum) were randomly assigned to one of two treatment groups. In group 1 (n = 31; WE1), lambs were separated from their dams 21 days prior to introduction to rams (RI). In group 2 (n = 25; TSE1), lambs were temporarily removed from the ewes for 3 days, beginning at ram introduction and then reunited with their dams for the next 24 days – after which they were permanently weaned. In Experiment 2, lactating ewes (n = 58; 75.7 ± 1.2 days postpartum) were randomly assigned according to parity and number of lambs suckling to one of 3 weaning systems. Ewes in group 1 (n = 29) were separated from their lambs 17 days prior to RI (WE2). Ewes in group 2 were temporarily separated from their lambs for 3 days, beginning at RI. Lambs were reunited with their dams for the remainder of the 50 day breeding period (n = 13; TSE2). Ewes in group 3 remained with their lambs throughout the breeding period (n = 16; UW). Date of lambing, number of lambs born, birth weight of the individual lambs and postnatal mortality up to day 60 post lambing were recorded in both experiments. 2.3. Effect of the weaning system on the growth of the lambs Two experiments were conducted to evaluate the effect of time of weaning on the growth of lambs. In Experiment 1, lambs born in June 2006 (n = 110) were randomly assigned to be weaned early (EW1; 75.6 ± 1.0 days of age; n = 56) or late (110 days later; LW1; 186.3 ± 1.0 days of age; n = 54). Half of the lambs in the late weaned group were temporarily separated from their dams for 3 days (at approximately 90 days of age). Temporary weaning did not affect the pattern of growth of these lambs, so data for both sets of late weaned lambs were pooled. Lambs were weighed at birth, at early weaning (EW1; P0) and at days 17, 46, 110 and 138 (P17, P46, P75, P110 and P138, respectively). Experiment 2 was similar to Experiment 1, except that lambs in the early weaned group were removed from their dams at an older age and the temporary lamb removal treatment was excluded. Briefly, lambs born in March 2007 (n = 118; 103.6 ± 1.5 days of
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2.4. Data and statistical analysis
220 200 180
Average Daily Gain, (g/d)
age; 19.5 ± 0.5 kg) were randomly allotted according to their parity and number of lambs suckling, to be weaned early (EW2; n = 63; 107.9 ± 1.7 days of age) or late (LW2; n = 55; 159 ± 2.1 days of age). Lambs were weighed at birth, at early weaning (EW2; P0) and 26, 60 and 85 days later (P0, P26, P60, and P85, respectively). Live weight changes and ADG from birth to early weaning and during all the subsequent periods, and the overall weight gain during each trial were recorded. Lamb mortality was recorded from initial weaning in early-weaned lambs, until the end of the observation period, which was approximately one month after the weaning of lambs in the late-weaned group.
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160 140 120 100 80 60 40
3. Results The reproductive performance of the ewes for Experiments 1 and 2 is set out in Table 1. In Experiment 1, the lambing interval was significantly longer (P < 0.001) in the TSE1 ewes, compared to ewes weaned prior to RI (WE1). All other reproductive performance variables were not affected by the time of weaning. In Experiment 2, there was a tendency for more ewes to lamb in the UW, than in the WE2-group. The weaning system used did not affect any other reproductive performance variables in Experiment 2 (Table 1). In Experiment 1, the overall ADG tended to be greater in the late weaning (LW1), compared to early-weaned lambs (EW1; Table 2). The ADG of the lambs showed a significant quadratic period × treatment interaction (P < 0.001). The ADG of lambs in the LW1 group demonstrating a linear decline between periods P0 through to P138. The ADG of lambs in the EW1 group declined continuously between the periods P0 and P75. Thereafter it increased between periods P75 and P110 and P110 and P138 (Fig. 1). ADG was higher for the periods P46 and P75 (P < 0.01) and lower in the period P17 (P < 0.05) and P138 (P < 0.001) respectively, in the late-weaned, compared to the early-weaned lambs (Fig. 1).
LW1 - late weaning
20
EW1 - early weaning
0 P0
P17
P46
P75
P110
P138
Period to weaning (days) Fig. 1. Average daily gain (g/day) in early-weaned (EW1) and late-weaned lambs (LW1) in Experiment 1.
In Experiment 2, the overall average daily gain (ADG) was significantly higher in the LW2, than in the EW2lambs (P < 0.01; 98.3 ± 6 and 124.4 ± 5 g/day for the EW2 and LW2-lambs, respectively; Table 2). A significant quadratic period × treatment interaction (P < 0.001; Fig. 3) was recorded, regarding ADG. The ADG of the EW2-lambs declined after weaning at P26, continued to decline at a decreasing rate until P60, followed by an increased in ADG at the period P85. The ADG of LW2-lambs did not change significantly between the periods P0 through to P60, but declined significantly following weaning (P < 0.001). A significant effect of period and period × weaning time interaction (P < 0.001) in live weight was recorded in Experiments 1 and 2 (Figs. 2 and 4). In Experiment 1, the live weight of the lambs increased throughout the experiment, in both treatment groups (Fig. 2). Weights were similar in the P0–P46 period, but higher in LW1- compared to EW1-lambs at P75 (3.15 ± 1.0 kg; P < 0.001), P110 (3.76 ± 1.0 kg; P < 0.001) and P138 (2.0 kg ± 1.0; P < 0.05). In Experiment 2, the live weight difference of the lambs 40
35
30
Liveweight, (kg)
An analysis of variance (ANOVA) was conducted to determine the effect of the weaning system on the reproductive performance, using the GLM procedure of SAS (SAS, 1996). The main effect was weaning system (WE1, TSE1 and WE2, TSE2 and UW for Experiments 1 and 2, respectively) and response variables included prolificacy (number of lambs born per ewe lambing), the interval from ram introduction to lambing, the mean lambing day (day lambed during the lambing period), lambing interval (number of days between two successive lambings) and birth weight of the lambs. The effect of the weaning system on the proportion of ewes lambing and lamb mortality was evaluated by Chi-square, using the PROC FREQ procedure of SAS. An ANOVA was used to determine the effect of time of weaning on the overall weight gain, ADG and final weight. Growth data (live weight and ADG) were analyzed using repeated measures PROC MIXED (SAS Inst. Inc. Cary, NC). The model to test for the main effects of treatment, period, and treatment X period interaction, included the fixed effects of time of weaning (EW1 vs LW1, Experiment 1; EW2 vs LW2, Experiment 2), period (P0, P17, P46, P75, P110 and P138 Experiment 1; P0, P26, P60, and P85 Experiment 2) and the period × time of weaning interaction, with period as the repeated term. The autoregressive heterogeneous structure was utilized to estimate the covariance. In Experiment 2 no differences were detected between late weaned lambs, with or without prior temporary separation. Therefore the data for these two groups were pooled (LW2). The slope responses for period (i.e. linear vs quadratic effects) and their interaction with treatment were assessed using a polynomial contrast – using the same model, except that period was considered to be a continuous variable (AlTrad et al., 2010). Significance was determined at a confidence level of P ≤ 0.05.
25
20
15
10
5
EW1 - early weaning LW1 - late weaning
0 P0
P17
P46
P75
P110
P138
Period to weaning (days) Fig. 2. Live weight (kg) of early-weaned (EW1) and late-weaned lambs (LW1) in Experiment 1.
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Table 1 Effect (mean ± SE) of different times of weaning relative to the breeding period on the subsequent reproductive performance of ewes. Experiment 1
N Ewes lambing, % Prolificacy Lamb birth weight, kg Ram to lamb, days Lambing day Lambing interval, days
Experiment 2
Weaned (WE)
Un-weaned with temporary separation (TSE1)
Weaned (WE2)
Un-weaned with temporary separation (TSE2)
Un-weaned (UW)
31 96.8 ± 4.3 2.1 ± 0.2 3.0 ± 0.1 152.4 ± 1.5 10.4 ± 1.5 247.1 ± 1.6a
25 90.2 ± 5.0 2.1 ± 0.2 2.9 ± 0.1 154.2 ± 1.9 12.2 ± 1.9 249.3 ± 2.0b
29 87.8 ± 5.3 2.0 ± 0.2 2.9 ± 0.1 171.3 ± 2.3 19.3 ± 2.2 262.7 ± 2.5
13 95.8 ± 7.7 2.5 ± 0.2 2.5 ± 0.1 167.6 ± 3.0 15.8 ± 2.9 262.3 ± 3.4
16 103 ± 7.0 2.1 ± 0.2 2.7 ± 0.1 168.2 ± 2.7 16.8 ± 2.6 262.3 ± 3.1
Means with different superscripts within a row differ significantly (P < 0.001).
Table 2 Effect (mean ± SE) of time of weaning on the growth and mortality rate of lambs. Experiment 1
N Initial age, days Actual age at weaning, days Final age, days Initial weight, kg Final weight, kg Average daily gain, g/day Total weight gain, kg Mortality rate, %
Experiment 2
Early weaned (EW1)
Late weaned (LW1)
Early weaned (EW2)
Late weaned (LW2)
56 75.6 ± 1.0 75.6 ± 1.0a 213.6 ± 1.0 16.8 ± 0.5 31.8 ± 0.9 107.2 ± 5.5 14.8 ± 0.8 22.2 ± 4.4a
54 76.3 ± 1.0 186.3 ± 1.0b 214.3 ± 1.0 16.9 ± 0.5 33.1 ± 0.8 118.2 ± 4.8 16.3 ± 0.7 3.6 ± 4.3b
63 107.9 ± 1.7c 107.9 ± 1.7a 192.9 ± 1.0c 20.0 ± 0.8 28.4 ± 0.9 98.3 ± 5.5a 8.4 ± 0.4a 1.6 ± 2.3
55 102.3 ± 1.6d 159 ± 2.1b 187.3 ± 1.0d 19.0 ± 0.8 29.6 ± 0.8 124.4 ± 4.9b 10.6 ± 0.4b 5.7 ± 2.5
Means with different superscripts within a row differ significantly: ab P < 0.01, cd P < 0.05.
(Fig. 4) tended to be higher in the LW2, than the EW2 lambs, at P60 (1.8 ± 1.1 kg), but this was not different at P85 (final weight). The total weight gain tended to be higher in the late-weaned, compared to the early-weaned lambs in Experiment 1. It was significantly higher (P < 0.01) in the LW2, compared to the EW2-lambs in Experiment 2 (8.4 ± 0.4 kg vs 10.6 ± 0.4 kg) (Table 2). The mean mortality rates were 10.4 ± 6.0%, 4.0 ± 3.7% for lambs in Experiments
1 and 2, respectively. The mortality rate being significantly higher (P < 0.01) in the early weaned, compared to the lateweaned lambs in Experiment 1, but not in Experiment 2 (Table 2).
35
30 180 25
160
Liveweight, (kg)
Average Daily Gain, (g/d)
140 120 100
20
15
80 10
60 40
5 LW2 - late weaning
LW2 - late weaning
20
EW2 - early weaning
EW2 - early weaning
0 P0
P26
P60
P85
Period to weaning (days) Fig. 3. Average daily gain (g/day) in early-weaned (EW2) and late-weaned lambs (LW2) in Experiment 2.
0 P0
P26
P60
P85
Period to weaning (days) Fig. 4. Live weight (kg) of early-weaned (EW2) and late-weaned lambs (LW2) in Experiment 2.
M. Knights et al. / Small Ruminant Research 103 (2012) 205–210
4. Discussion Systems to increase the frequency of lambing in order to enhance ewe-productivity in both temperate (Wheaton et al., 1992; Lewis et al., 1996) and tropical hair sheep breeds (Rodríguez et al., 1998; Rastogi, 2001; Ronquillo et al., 2008), have utilized early weaning. In order to allow ewes to bypass the inhibitory effects of the suckling stimulus on fertility, and or to reduce nutritional anestrous, associated with the high metabolic demand of lactation. In the present study, weaning after day 70 postpartum, before or after introduction of the rams, did not improve any of the key reproductive performance indices. Ewes, whether pre-weaned, temporarily weaned at the time of ram introduction or continuously suckled recorded a high level of reproductive performance. The percentage of ewes lambing was higher than 90%, and ewes had an average prolificacy of 2.0 and lambing interval of less than 9 months. These high levels of fertility suggest that most ewes had emerged from the postpartum period of reproductive quiescence, and were displaying regular estrous cycles at the onset of the breeding period. In previous reports, ewes under temperate conditions giving birth during the stimulatory photoperiod of autumn, escaped the inhibitory effects of lactation/suckling and returned to cyclicity by 32 days postpartum (Lewis and Bolt, 1983). Moreover, the involution of the uterus of the ewe is complete by day 40 (O’Shea and Wright, 1984; Hauser and Bostedt, 2002; Gray et al., 2003), which suggests the ewe is capable of showing regular estrous cycles, conceiving and maintaining a pregnancy by day 40 postpartum. These studies and the present findings indicate that ewes, and in particular aseasonal breeds, such as the BBB, when provided with an optimum nutritional and a favorable photoperiodic environment do not require weaning to resume cyclicity and show high levels of fertility when bred after day 70 postpartum. Lambs that were weaned later tended to or showed significantly faster growth rates (ADG), and higher live weights and total weight gain. The magnitude of the differences in ADG, weight gain and live weight was greatest in the period immediately prior to weaning of the lambs in the late weaned groups. These observations are consistent with the findings of DeNicolo et al. (2006), who reported lower live weights and ADG at 4 months of age in lambs weaned at 69 days, compared to those weaned at 91 days of ˜ et al. (2001) found unweaned lambs to record age. Caneque higher growth rates and a lower concentrate intake up to slaughter, compared to lambs weaned at 65 or 45 days of age when raised on pasture with ad libitum access to concentrate feed. Lambs weaned at 65 days of age generally recorded an intermediate ADG. The ADG attained in the present study ranged between 98–107 and 118–124 g/day in early weaned and late weaned lambs, respectively. This was significantly higher than the 56–73 g/day recorded in BBB lambs, weaned at 2 months of age, and fed a grain-protein supplement between weaning and marketing (Rastogi, 2001; Wildeus et al., 2005). This result indicates that significant improvements in pre-market weight gains can be achieved by delaying or not weaning lambs prior to market.
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Delaying weaning until after 90 days of age to allow lambs to develop the capacity to consume adequate amounts of dry matter to meet their nutrient requirements has generally been recommended. In the present study, an accelerated decline in growth rate occurred, even when weaning occurred at 108 days of age (EW2; Experiment 2), or after late weaning at 186 and 159 days of age (LW1, LW2; Experiments 1 and 2, respectively). These decreases in the growth rate of late-weaned lambs, together with recovery in the ADG of early weaned lambs, reduced the differences in growth and weight of the lambs towards the end of the trial. This resulted in small differences (Experiments 1 and 2) in the overall performance of the lambs. Live weights of late-weaned lambs have been reported to remain higher than those of early-weaned lambs, one month after weaning (DeNicolo et al., 2006). This however was associated with a declining ADG in the late-weaned lambs, and an increasing ADG in the early weaned lambs – as observed in the present study. These observations may in part explain why no difference or higher growth rates in early, compared to late-weaned lambs, have been reported in certain studies in which weaning occurred prior to 90–120 days of age in both the early and late weaned groups (Poe et al., 1969; Abou Ward et al., 2008; Aksakal et al., 2009). The present findings indicate that a weaning-associated decrease in growth rate can occur late in the growth phase of the lambs – which can reduce or negate the initial benefits gained by delaying weaning. In contrast, maintaining contact with dams throughout the growing period increased body weight of lambs at market/slaughter, ˜ compared to their weaned counterparts (Caneque et al., 2001). The exact reason(s) for the abrupt decline in growth rate of late weaned lambs is not clear. A decrease in growth rate following early weaning has generally been attributed to the inability of the lamb to rapidly modify the secretions of the gastro-intestinal tract – to facilitate adequate consumption and utilization of dry dietary products to meet the nutritional requirements – which the consumption of milk provided, prior to weaning (Guilloteau et al., 2009). However, milk production in BBB ewes has been estimated to be low (less than 0.2 kg/day) at 100 days in milk, and this may not be a significant source of nutrients in lambs weaned after day 100 postpartum (Godfrey et al., 1997). Additionally, feed intake decreases immediately after weaning and then recovers (Poe et al., 1969). This tendency was greater in lambs weaned early, than those weaned later (8 weeks vs 12 weeks) (Abou Ward et al., 2008) and 4 weeks vs 8 weeks (Holcombe et al., 1994). This suggests feed intake to recover rapidly after weaning, and not be a limiting factor in lambs weaned early in life. Some evidence does however exist to support that continued suckling can reduce the rate of transition of the gastrointestinal tract (GIT) from the pre-ruminant to ruminant state. Thus allowing a greater proportion of starch to reach the small intestine, where digestion is more efficient than in the rumen. In contrast, weaning accelerates the development of the GIT and modifies the digestive secretions from a pre-ruminant to a ruminant state (Guilloteau et al., 2009). Thereby enhancing the efficiency of utilization of roughage diets. This may in part explain the better growth
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performance of unweaned lambs, when fed ˜ grain/concentrate diets (Caneque et al., 2001). Also, the better performance of weaned lambs placed on a post-weaning diet consisting only of roughage/pasture (Notter et al., 1991). The mortality rate of lambs was higher in early weaned, compared to late weaned lambs in Experiment 1, but not in Experiment 2. The mortality rate was highest in lambs weaned early in Experiment 1, and lowest in Experiment 2, when weaning occurred later (after 3.5 months in the early weaned group). High pre- and post-weaning mortality rates were also reported for hair sheep breeds in the tropics (Rastogi, 2001; Turkson and Sualisu, 2005). The findings in this study are consistent with those of Hatcher et al. (2010) who observed significantly higher mortalities in lambs that were lighter at weaning. These findings indicate that a significant loss in productivity may occur through increased lamb mortalities associated with the early weaning of lambs. To conclude, it can be said that the rearing of lambs with ewes prior to and during the breeding period did not negatively impact on the subsequent reproductive performance of the dams. Conversely, weaning BBB lambs increased the mortality rate of the lambs and resulted in an accelerated decline in lamb growth rates, regardless of the age at weaning. Management systems in which ewes are re-bred 2.5–3.5 months after lambing and lambs are reared continuously with ewes until market at 6.5–7.5 months of age may offer producers an opportunity to maximize the productivity of the ewes in terms of the kg of lamb marketed annually. Acknowledgements This research was supported by the Department of Food Production, University of the West Indies St. Augustine Sheep Project. The authors would like to thank Mr. Errol Fullerton and Darren Wong for their assistance in data collection and general management of the sheep flock. References Abou Ward, G.A., Tawila, M.A., Sawsan, M., Gad, A.A., El-Naggar, A., ElNaggar, S., 2008. Effect of weaning age on lamb’s performance. World J. Agric. Sci. 4, 569–573. Aksakal, V., Emsen, E., Ozdemir, M., Macit, M., 2009. Effects of various ages of weaning on growth performance of morkaraman lambs. J. Anim. Vet. Adv. 8, 1551–1554. Al-Trad, B., Wittek, T., Penner, G.B., Reisberg, K., Gäbel, G., Fürll, M., Aschenbach, J.R., 2010. Expression and activity of key hepatic gluconeogenesis enzymes in response to increasing intravenous infusions of glucose in dairy cows. J. Anim. Sci. 88, 2998–3008. ˜ V., Velasco, S., Díaz, M., Pérez, C., Huidobro, F., Lauzurica, S., ManCaneque, zanares, C., González, J., 2001. Effect of weaning age and slaughter weight on carcass and meat quality of Talaverana breed lambs raised at pasture. Anim. Sci. 73, 85–95.
DeNicolo, G., Morris, S.T., Kenyon, P.R., Morel, P.C.H., 2006. Effect of weaning pre- or post-mating on performance of spring-mated ewes and their lambs in New Zealand. N. Z. J. Agric. Res. 49, 255–260. Godfrey, R.W., Gray, M.L., Collins, J.R., 1997. Lamb growth and milk production of hair and wool sheep in a semi-arid tropical environment. Small Rumin. Res. 24, 77–83. Gray, C.A., Stewart, M.D., Johnson, G.A., Spencer, T.E., 2003. Postpartum uterine involution in sheep: histoarchitecture and changes in endometrial gene expression. Reproduction 125, 185–198. Guilloteau, P., Zabielski, R., Blum, J.W., 2009. Gastrointestinal tract and digestion in the Young ruminant: ontogenesis, adaptations, consequences and manipulations. J. Physiol. Pharm. 60 (Suppl. 3), 37–46. Hatcher, S., Eppleston, J., Thornberry, K.J., Watt, B., 2010. High Merino weaner survival rates are a function of weaning weight and positive post-weaning growth rates. Anim. Prod. Sci. 50, 465–472. Hauser, B., Bostedt, H., 2002. Ultrasonographic observations of the uterine regression in the ewe under different obstetrical conditions. J. Vet. Med. Physiol. Pathol. Clin. Med. 49, 511–516. Hawk, H.W., Cooper, B.S., 1977. Sperm transport into the cervix of the ewe after regulation of estrus with prostaglandin or progestogen. J. Anim. Sci. 44, 638–644. Holcombe, D.W., Hanks, D.R., Krystal, L.J., Jud-Kins, M.B., Niksic, G.M., Hallford, D.M., 1994. Effect of Age at Weaning on intake, insulin-like growth factor I, thyroxine, triiodothyronine, metabolite profiles and growth performance in young lambs. Sheep Res. J. 10, 25–34. Jenkins, T.G., 1986. Postweaning performance and carcass characteristics of crossbred ewe lambs produced in accelerated or annual lambing systems. J. Anim. Sci. 63, 1063–1071. Lewis, G.S., Bolt, D.J., 1983. Effect of suckling on postpartum changes in 13,14- dihydro-15-keto- PGF2 alpha and progesterone and induced release of gonadotropins in autumn-lambing ewes. J. Anim. Sci. 57, 673–682. Lewis, R.M., Notter, D.R., Hogue, D.E., Magee, B.H., 1996. Ewe fertility in the STAR accelerated lambing system. J. Anim. Sci. 74, 1511–1522. Notter, D.R., Kelly, R.F., McClaugherty, F.S., 1991. Effects of ewe breed and management system on efficiency of lamb production: II Lamb growth, survival and carcass characteristics. J. Anim. Sci. 69, 22–33. Nugent 3rd., R.A., Jenkins, T.G., 1991. Effects of alternative lamb production systems, terminal sire breed, and maternal line on ewe productivity and its components. J. Anim. Sci. 69, 4777–4792. O’Shea, J.D., Wright, P.J., 1984. Involution and regeneration of the endometrium following parturition in the ewe. Cell Tissue Res. 236, 477–485. Poe, S.E., Glimp, H.A., Deweese, W.P., Mitchell Jr., G.E., 1969. Effect of preweaning diet on the growth and development of early-weaned lambs. J. Anim. Sci. 28, 401–405. Rastogi, R.K., 2001. Production performance of Barbados Blackbelly sheep in Tobago, West Indies. Small Rumin. Res. 41, 171–175. Rodríguez, R.O.L., Heredia, A.M., Quintal, F.J., Velazquez, M.A., 1998. Productivity of Pelibuey and Blackbelly ewes mated at yearly and 8-monthly intervals over six years. Small Rumin. Res. 30, 177–184. Ronquillo, J.C., Martinez, A.P., Perez, C.M., Sandoval, B.F., Martin, G.B., Valencia, J., Gallegos Sanchez, J., 2008. Prevention of suckling improves postpartum reproductive responses to hormone treatments in Pelibuey ewes. Anim. Reprod. Sci. 107, 85–93. Turkson, P.K., Sualisu, M., 2005. Risk factors for lamb mortality in Sahelian sheep on a breeding station in Ghana. Trop. Anim. Health Prod. 37 (1), 49–64. Warren Jr., J.E., Kiesling, D.O., Akinbami, M.A., Price, E.A., Meredith, S., 1989. Conception rates in early postpartum ewes bred naturally or by intrauterine insemination. J. Anim. Sci. 67, 2056–2059. Wheaton, J.E., Windels, H.F., Johnston, L.J., 1992. Accelerated lambing using exogenous progesterone and the ram effect. J. Anim. Sci. 70, 2628–2635. Wildeus, S., Turner, K.E., Collins, J.R., 2005. Growth performance of Barbados Blackbelly, Katahdin and St. Croix hair sheep lambs fed pasture-or hay-based Diets. Sheep Goat Res. J. 20, 37–41.
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Small Ruminant Research journal homepage: www.elsevier.com/locate/smallrumres
Effect of time of weaning on the reproductive performance of Barbados Blackbelly ewes and lamb growth reared in the tropics M. Knights a,∗ , N. Siew a,1 , R. Ramgattie a,1 , D. Singh-Knights b,2 , G. Bourne c a b c
University of the West Indies, Department of Food Production, St. Augustine, Trinidad and Tobago University of the West Indies, Department of Agriculture Economics and Extension, St. Augustine, Trinidad and Tobago University of the West Indies, School of Veterinary Medicine, Mount Hope, Trinidad and Tobago
a r t i c l e
i n f o
Article history: Received 19 April 2011 Received in revised form 9 September 2011 Accepted 16 September 2011 Available online 10 October 2011 Keywords: Weaning Sheep Reproduction Average daily gain
a b s t r a c t The effects of time of weaning on subsequent reproductive performance of ewes and the growth of lambs were evaluated in Barbados Blackbelly hair sheep, under a tropical photoperiod. Two experiments were conducted to assess the effect of time of weaning on subsequent reproductive performance of the ewe. In Experiment 1, lactating ewes (n = 56) were weaned early (WE1; 72.6 ± 1.3 days postpartum; n = 31), 21 days prior to introduction to the rams (RI) – or not weaned prior to the breeding period, but temporarily removed from their lambs (n = 25) for 3 days – beginning at ram introduction and then weaned 24 days later (TSE1; 121.2 ± 1.3 days postpartum). In Experiment 2, ewes were either separated from their lambs (n = 29), 17 days prior to ram introduction (RI; WE2; 75.7 ± 1.2 days postpartum) remained with their lambs during the entire breeding period (UW; n = 16), or their lambs temporarily removed for 3 days – beginning at ram introduction (RI) and then re-joined with their dams (n = 13; TSE2). The proportion of ewes lambing, interval from RI to lambing, lambing day during lambing period and prolificacy were not affected by treatment. The lambing interval recorded was longer in late weaned ewes in Experiment 1, but time of weaning had no effect in Experiment 2. To assess the effect of time of weaning on lamb growth, two experiments were conducted in which lambs were weaned either early (EW; 76 or 108 days of age for Experiments 1 and 2, respectively) or late (LW; 186 and 159 days of age for Experiments 1 and 2, respectively). Lambs were weighed at birth, at weaning and at monthly intervals until 1 month following the separation of the late weaned animals from their dams. The effect of time of weaning on ADG showed a significant quadratic period × treatment interaction (P < 0.001). The ADG of the EW-lambs declined after weaning for approximately 2 months, followed by an increase in ADG. In contrast the ADG in the LW-lambs did not change significantly or declined slowly prior to weaning, but showed a sharp decline following weaning. The overall ADG and total live weight gain tended to be or was higher (P < 0.01) in compared to the EW lambs of Experiments 1 and 2, respectively – despite the recovery in ADG in EW-lambs and the decline in ADG, following weaning in LW-lambs. A significant period × treatment interaction (P < 0.001) regarding live weight was recorded, with the difference in live weights being greatest immediately prior to weaning in the LW-lambs. The mortality rate of the lambs was significantly higher (P < 0.01) in the EW- compared to LW-lambs, in Experiment 1 only. Weaning lambs prior to or after
∗ Corresponding author. Current address: Division of Animal and Nutritional Sciences, West Virginia University, PO Box 6108, Morgantown, WV 26506-6108, United States. Tel.: +1 304 293 1946; fax: +1 304 293 2232. E-mail address: [email protected] (M. Knights). 1 Current address: BioSciences Agriculture and Food Technologies (BAFT), University of Trinidad and Tobago, Eastern Caribbean Institute of Agriculture and Forestry (ECIAF) Campus, Centeno, Trinidad and Tobago. 2 Current address: Division of Natural Resources and Design, West Virginia University, PO Box 6108, Morgantown, WV 26506-6108, United States. 0921-4488/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.smallrumres.2011.09.042
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the breeding period did not improve the subsequent reproductive performance of dams, but increased the mortality rate of lambs in some cases, and resulted in an accelerated decline in growth rates, regardless of the age of weaning in hair sheep reared under a tropical photoperiod. Management systems in which the ewes are re-bred 2.5–3.5 months after lambing, and lambs are reared with the ewes until market at 6.5–7.5 months of age provide an opportunity to maximize productivity of ewes, in relation to kg lamb marketed annually. © 2011 Elsevier B.V. All rights reserved.
1. Introduction Productivity of the ewe can be improved by increasing the frequency of lambing. However, the suppressive effect of lactation, superimposed on inhibitory photoperiod, limits the productivity of most ewes in the temperate regions, to one lambing season per year. Attempts to accelerate the frequency of lambing have traditionally relied on highinput management systems that may involve the early weaning of lambs, with or without the use of hormonebased estrous induction therapies (Wheaton et al., 1992; Lewis et al., 1996; Rodríguez et al., 1998). These approaches have yielded moderate or little improvement in ewe productivity, as measured by the frequency of lambing and kg lamb weaned per year (Nugent and Jenkins, 1991). Additionally, early weaning systems increased post weaning lamb management costs, associated with rearing lighter feeder/nursery lambs (Jenkins, 1986), lower post weaning weights (Rastogi, 2001; Wildeus et al., 2005; DeNicolo et al., 2006) and increased post-weaning lamb mortalities (Hatcher et al., 2010). Postpartum uterine involution in sheep is completed by days 30–40 after lambing (O’Shea and Wright, 1984; Hauser and Bostedt, 2002; Gray et al., 2003). The first postpartum estrus being detected by day 32 in a large proportion of suckled and non-suckled ewes lambing during the stimulatory photoperiod of autumn (Lewis and Bolt, 1983). Conception rates did not differ between dry and lactating ewes, but increased as the postpartum interval increased from 30 to 50 days (Warren et al., 1989). These results indicate that, in the absence of an inhibitory long photoperiod, fertile breeding and the establishment of pregnancy can occur in the ewe as early as day 40 postpartum, without the necessity for weaning. Tropical hair sheep breeds have shown a reduced sensitivity to the inhibitory effects of long day photoperiod under temperate environments and generally, breed year round under the relatively constant photoperiod of the tropical conditions (Rastogi, 2001). Therefore, under tropical conditions without the inhibitory effects of season, ewes of the hair sheep breeds may be able to rebreed following a short postpartum period, while suckling their young. However, the effects of extended suckling periods on the reproductive performance of the ewe and growth rates of their lambs have not been fully studied in the tropics. Therefore, the objectives of this study were to determine the effect of lactation/suckling during the breeding period and early pregnancy on the reproductive performance of the Barbados Blackbelly (BBB) ewe, and to determine the effect on live weights and growth rates of their lambs up to marketing or slaughter weight.
2. Materials and methods 2.1. Animals and general management The animals used in this study were of at least 7/8 BBB cross-breds. Ewes were reared in barns on raised slatted floors at the University of the West Indies Field Station, located in Mount Hope, Trinidad and Tobago (10◦ 40 N, 61◦ 31 W). All animals were fed a diet of green forage ad libitum and supplemented with an 18% crude protein concentrate. Lambs were offered the concentrate ad libitum as a creep feed, prior to weaning, with free access following weaning. Following weaning lambs were maintained in barns with a spacing allowance of no less than 0.4 m2 per lamb and in groups of no more than 16. Rams were reared in a separate building prior to their introduction to the females. Breeding periods of 35 and 50 days were used in Experiments 1 and 2, respectively. Prior to introduction of the rams, all ewes were subjected to an estrous synchronization protocol, consisting of injections of progesterone (200 mg dissolved in corn oil, i.m., Sigma–Aldrich) on day −5 (d −5) and day −2.5 (d −2.5). This was followed by prostaglandin F2␣ injections (PGF2␣ , 2× 10 mg 3 h apart, i.m. Lutalyse® Pharmacia and UpJohn, NY) (Hawk and Cooper, 1977), on the day of ram introduction (d0). Rams were joined with ewes in all treatment groups on the same day (d0) at ewe to ram ratios of between 12:1 and 15:1. All rams used in the study were mature and fertility proven. However a breeding soundness examination had not been conducted prior to the experiment.
2.2. Effect of weaning on reproductive performance Two experiments were conducted to determine the effect of time of weaning relative to the breeding period on the reproductive performance of the ewes. In Experiment 1, lactating ewes (n = 56; 72.6 ± 1.3 days postpartum) were randomly assigned to one of two treatment groups. In group 1 (n = 31; WE1), lambs were separated from their dams 21 days prior to introduction to rams (RI). In group 2 (n = 25; TSE1), lambs were temporarily removed from the ewes for 3 days, beginning at ram introduction and then reunited with their dams for the next 24 days – after which they were permanently weaned. In Experiment 2, lactating ewes (n = 58; 75.7 ± 1.2 days postpartum) were randomly assigned according to parity and number of lambs suckling to one of 3 weaning systems. Ewes in group 1 (n = 29) were separated from their lambs 17 days prior to RI (WE2). Ewes in group 2 were temporarily separated from their lambs for 3 days, beginning at RI. Lambs were reunited with their dams for the remainder of the 50 day breeding period (n = 13; TSE2). Ewes in group 3 remained with their lambs throughout the breeding period (n = 16; UW). Date of lambing, number of lambs born, birth weight of the individual lambs and postnatal mortality up to day 60 post lambing were recorded in both experiments. 2.3. Effect of the weaning system on the growth of the lambs Two experiments were conducted to evaluate the effect of time of weaning on the growth of lambs. In Experiment 1, lambs born in June 2006 (n = 110) were randomly assigned to be weaned early (EW1; 75.6 ± 1.0 days of age; n = 56) or late (110 days later; LW1; 186.3 ± 1.0 days of age; n = 54). Half of the lambs in the late weaned group were temporarily separated from their dams for 3 days (at approximately 90 days of age). Temporary weaning did not affect the pattern of growth of these lambs, so data for both sets of late weaned lambs were pooled. Lambs were weighed at birth, at early weaning (EW1; P0) and at days 17, 46, 110 and 138 (P17, P46, P75, P110 and P138, respectively). Experiment 2 was similar to Experiment 1, except that lambs in the early weaned group were removed from their dams at an older age and the temporary lamb removal treatment was excluded. Briefly, lambs born in March 2007 (n = 118; 103.6 ± 1.5 days of
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2.4. Data and statistical analysis
220 200 180
Average Daily Gain, (g/d)
age; 19.5 ± 0.5 kg) were randomly allotted according to their parity and number of lambs suckling, to be weaned early (EW2; n = 63; 107.9 ± 1.7 days of age) or late (LW2; n = 55; 159 ± 2.1 days of age). Lambs were weighed at birth, at early weaning (EW2; P0) and 26, 60 and 85 days later (P0, P26, P60, and P85, respectively). Live weight changes and ADG from birth to early weaning and during all the subsequent periods, and the overall weight gain during each trial were recorded. Lamb mortality was recorded from initial weaning in early-weaned lambs, until the end of the observation period, which was approximately one month after the weaning of lambs in the late-weaned group.
207
160 140 120 100 80 60 40
3. Results The reproductive performance of the ewes for Experiments 1 and 2 is set out in Table 1. In Experiment 1, the lambing interval was significantly longer (P < 0.001) in the TSE1 ewes, compared to ewes weaned prior to RI (WE1). All other reproductive performance variables were not affected by the time of weaning. In Experiment 2, there was a tendency for more ewes to lamb in the UW, than in the WE2-group. The weaning system used did not affect any other reproductive performance variables in Experiment 2 (Table 1). In Experiment 1, the overall ADG tended to be greater in the late weaning (LW1), compared to early-weaned lambs (EW1; Table 2). The ADG of the lambs showed a significant quadratic period × treatment interaction (P < 0.001). The ADG of lambs in the LW1 group demonstrating a linear decline between periods P0 through to P138. The ADG of lambs in the EW1 group declined continuously between the periods P0 and P75. Thereafter it increased between periods P75 and P110 and P110 and P138 (Fig. 1). ADG was higher for the periods P46 and P75 (P < 0.01) and lower in the period P17 (P < 0.05) and P138 (P < 0.001) respectively, in the late-weaned, compared to the early-weaned lambs (Fig. 1).
LW1 - late weaning
20
EW1 - early weaning
0 P0
P17
P46
P75
P110
P138
Period to weaning (days) Fig. 1. Average daily gain (g/day) in early-weaned (EW1) and late-weaned lambs (LW1) in Experiment 1.
In Experiment 2, the overall average daily gain (ADG) was significantly higher in the LW2, than in the EW2lambs (P < 0.01; 98.3 ± 6 and 124.4 ± 5 g/day for the EW2 and LW2-lambs, respectively; Table 2). A significant quadratic period × treatment interaction (P < 0.001; Fig. 3) was recorded, regarding ADG. The ADG of the EW2-lambs declined after weaning at P26, continued to decline at a decreasing rate until P60, followed by an increased in ADG at the period P85. The ADG of LW2-lambs did not change significantly between the periods P0 through to P60, but declined significantly following weaning (P < 0.001). A significant effect of period and period × weaning time interaction (P < 0.001) in live weight was recorded in Experiments 1 and 2 (Figs. 2 and 4). In Experiment 1, the live weight of the lambs increased throughout the experiment, in both treatment groups (Fig. 2). Weights were similar in the P0–P46 period, but higher in LW1- compared to EW1-lambs at P75 (3.15 ± 1.0 kg; P < 0.001), P110 (3.76 ± 1.0 kg; P < 0.001) and P138 (2.0 kg ± 1.0; P < 0.05). In Experiment 2, the live weight difference of the lambs 40
35
30
Liveweight, (kg)
An analysis of variance (ANOVA) was conducted to determine the effect of the weaning system on the reproductive performance, using the GLM procedure of SAS (SAS, 1996). The main effect was weaning system (WE1, TSE1 and WE2, TSE2 and UW for Experiments 1 and 2, respectively) and response variables included prolificacy (number of lambs born per ewe lambing), the interval from ram introduction to lambing, the mean lambing day (day lambed during the lambing period), lambing interval (number of days between two successive lambings) and birth weight of the lambs. The effect of the weaning system on the proportion of ewes lambing and lamb mortality was evaluated by Chi-square, using the PROC FREQ procedure of SAS. An ANOVA was used to determine the effect of time of weaning on the overall weight gain, ADG and final weight. Growth data (live weight and ADG) were analyzed using repeated measures PROC MIXED (SAS Inst. Inc. Cary, NC). The model to test for the main effects of treatment, period, and treatment X period interaction, included the fixed effects of time of weaning (EW1 vs LW1, Experiment 1; EW2 vs LW2, Experiment 2), period (P0, P17, P46, P75, P110 and P138 Experiment 1; P0, P26, P60, and P85 Experiment 2) and the period × time of weaning interaction, with period as the repeated term. The autoregressive heterogeneous structure was utilized to estimate the covariance. In Experiment 2 no differences were detected between late weaned lambs, with or without prior temporary separation. Therefore the data for these two groups were pooled (LW2). The slope responses for period (i.e. linear vs quadratic effects) and their interaction with treatment were assessed using a polynomial contrast – using the same model, except that period was considered to be a continuous variable (AlTrad et al., 2010). Significance was determined at a confidence level of P ≤ 0.05.
25
20
15
10
5
EW1 - early weaning LW1 - late weaning
0 P0
P17
P46
P75
P110
P138
Period to weaning (days) Fig. 2. Live weight (kg) of early-weaned (EW1) and late-weaned lambs (LW1) in Experiment 1.
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Table 1 Effect (mean ± SE) of different times of weaning relative to the breeding period on the subsequent reproductive performance of ewes. Experiment 1
N Ewes lambing, % Prolificacy Lamb birth weight, kg Ram to lamb, days Lambing day Lambing interval, days
Experiment 2
Weaned (WE)
Un-weaned with temporary separation (TSE1)
Weaned (WE2)
Un-weaned with temporary separation (TSE2)
Un-weaned (UW)
31 96.8 ± 4.3 2.1 ± 0.2 3.0 ± 0.1 152.4 ± 1.5 10.4 ± 1.5 247.1 ± 1.6a
25 90.2 ± 5.0 2.1 ± 0.2 2.9 ± 0.1 154.2 ± 1.9 12.2 ± 1.9 249.3 ± 2.0b
29 87.8 ± 5.3 2.0 ± 0.2 2.9 ± 0.1 171.3 ± 2.3 19.3 ± 2.2 262.7 ± 2.5
13 95.8 ± 7.7 2.5 ± 0.2 2.5 ± 0.1 167.6 ± 3.0 15.8 ± 2.9 262.3 ± 3.4
16 103 ± 7.0 2.1 ± 0.2 2.7 ± 0.1 168.2 ± 2.7 16.8 ± 2.6 262.3 ± 3.1
Means with different superscripts within a row differ significantly (P < 0.001).
Table 2 Effect (mean ± SE) of time of weaning on the growth and mortality rate of lambs. Experiment 1
N Initial age, days Actual age at weaning, days Final age, days Initial weight, kg Final weight, kg Average daily gain, g/day Total weight gain, kg Mortality rate, %
Experiment 2
Early weaned (EW1)
Late weaned (LW1)
Early weaned (EW2)
Late weaned (LW2)
56 75.6 ± 1.0 75.6 ± 1.0a 213.6 ± 1.0 16.8 ± 0.5 31.8 ± 0.9 107.2 ± 5.5 14.8 ± 0.8 22.2 ± 4.4a
54 76.3 ± 1.0 186.3 ± 1.0b 214.3 ± 1.0 16.9 ± 0.5 33.1 ± 0.8 118.2 ± 4.8 16.3 ± 0.7 3.6 ± 4.3b
63 107.9 ± 1.7c 107.9 ± 1.7a 192.9 ± 1.0c 20.0 ± 0.8 28.4 ± 0.9 98.3 ± 5.5a 8.4 ± 0.4a 1.6 ± 2.3
55 102.3 ± 1.6d 159 ± 2.1b 187.3 ± 1.0d 19.0 ± 0.8 29.6 ± 0.8 124.4 ± 4.9b 10.6 ± 0.4b 5.7 ± 2.5
Means with different superscripts within a row differ significantly: ab P < 0.01, cd P < 0.05.
(Fig. 4) tended to be higher in the LW2, than the EW2 lambs, at P60 (1.8 ± 1.1 kg), but this was not different at P85 (final weight). The total weight gain tended to be higher in the late-weaned, compared to the early-weaned lambs in Experiment 1. It was significantly higher (P < 0.01) in the LW2, compared to the EW2-lambs in Experiment 2 (8.4 ± 0.4 kg vs 10.6 ± 0.4 kg) (Table 2). The mean mortality rates were 10.4 ± 6.0%, 4.0 ± 3.7% for lambs in Experiments
1 and 2, respectively. The mortality rate being significantly higher (P < 0.01) in the early weaned, compared to the lateweaned lambs in Experiment 1, but not in Experiment 2 (Table 2).
35
30 180 25
160
Liveweight, (kg)
Average Daily Gain, (g/d)
140 120 100
20
15
80 10
60 40
5 LW2 - late weaning
LW2 - late weaning
20
EW2 - early weaning
EW2 - early weaning
0 P0
P26
P60
P85
Period to weaning (days) Fig. 3. Average daily gain (g/day) in early-weaned (EW2) and late-weaned lambs (LW2) in Experiment 2.
0 P0
P26
P60
P85
Period to weaning (days) Fig. 4. Live weight (kg) of early-weaned (EW2) and late-weaned lambs (LW2) in Experiment 2.
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4. Discussion Systems to increase the frequency of lambing in order to enhance ewe-productivity in both temperate (Wheaton et al., 1992; Lewis et al., 1996) and tropical hair sheep breeds (Rodríguez et al., 1998; Rastogi, 2001; Ronquillo et al., 2008), have utilized early weaning. In order to allow ewes to bypass the inhibitory effects of the suckling stimulus on fertility, and or to reduce nutritional anestrous, associated with the high metabolic demand of lactation. In the present study, weaning after day 70 postpartum, before or after introduction of the rams, did not improve any of the key reproductive performance indices. Ewes, whether pre-weaned, temporarily weaned at the time of ram introduction or continuously suckled recorded a high level of reproductive performance. The percentage of ewes lambing was higher than 90%, and ewes had an average prolificacy of 2.0 and lambing interval of less than 9 months. These high levels of fertility suggest that most ewes had emerged from the postpartum period of reproductive quiescence, and were displaying regular estrous cycles at the onset of the breeding period. In previous reports, ewes under temperate conditions giving birth during the stimulatory photoperiod of autumn, escaped the inhibitory effects of lactation/suckling and returned to cyclicity by 32 days postpartum (Lewis and Bolt, 1983). Moreover, the involution of the uterus of the ewe is complete by day 40 (O’Shea and Wright, 1984; Hauser and Bostedt, 2002; Gray et al., 2003), which suggests the ewe is capable of showing regular estrous cycles, conceiving and maintaining a pregnancy by day 40 postpartum. These studies and the present findings indicate that ewes, and in particular aseasonal breeds, such as the BBB, when provided with an optimum nutritional and a favorable photoperiodic environment do not require weaning to resume cyclicity and show high levels of fertility when bred after day 70 postpartum. Lambs that were weaned later tended to or showed significantly faster growth rates (ADG), and higher live weights and total weight gain. The magnitude of the differences in ADG, weight gain and live weight was greatest in the period immediately prior to weaning of the lambs in the late weaned groups. These observations are consistent with the findings of DeNicolo et al. (2006), who reported lower live weights and ADG at 4 months of age in lambs weaned at 69 days, compared to those weaned at 91 days of ˜ et al. (2001) found unweaned lambs to record age. Caneque higher growth rates and a lower concentrate intake up to slaughter, compared to lambs weaned at 65 or 45 days of age when raised on pasture with ad libitum access to concentrate feed. Lambs weaned at 65 days of age generally recorded an intermediate ADG. The ADG attained in the present study ranged between 98–107 and 118–124 g/day in early weaned and late weaned lambs, respectively. This was significantly higher than the 56–73 g/day recorded in BBB lambs, weaned at 2 months of age, and fed a grain-protein supplement between weaning and marketing (Rastogi, 2001; Wildeus et al., 2005). This result indicates that significant improvements in pre-market weight gains can be achieved by delaying or not weaning lambs prior to market.
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Delaying weaning until after 90 days of age to allow lambs to develop the capacity to consume adequate amounts of dry matter to meet their nutrient requirements has generally been recommended. In the present study, an accelerated decline in growth rate occurred, even when weaning occurred at 108 days of age (EW2; Experiment 2), or after late weaning at 186 and 159 days of age (LW1, LW2; Experiments 1 and 2, respectively). These decreases in the growth rate of late-weaned lambs, together with recovery in the ADG of early weaned lambs, reduced the differences in growth and weight of the lambs towards the end of the trial. This resulted in small differences (Experiments 1 and 2) in the overall performance of the lambs. Live weights of late-weaned lambs have been reported to remain higher than those of early-weaned lambs, one month after weaning (DeNicolo et al., 2006). This however was associated with a declining ADG in the late-weaned lambs, and an increasing ADG in the early weaned lambs – as observed in the present study. These observations may in part explain why no difference or higher growth rates in early, compared to late-weaned lambs, have been reported in certain studies in which weaning occurred prior to 90–120 days of age in both the early and late weaned groups (Poe et al., 1969; Abou Ward et al., 2008; Aksakal et al., 2009). The present findings indicate that a weaning-associated decrease in growth rate can occur late in the growth phase of the lambs – which can reduce or negate the initial benefits gained by delaying weaning. In contrast, maintaining contact with dams throughout the growing period increased body weight of lambs at market/slaughter, ˜ compared to their weaned counterparts (Caneque et al., 2001). The exact reason(s) for the abrupt decline in growth rate of late weaned lambs is not clear. A decrease in growth rate following early weaning has generally been attributed to the inability of the lamb to rapidly modify the secretions of the gastro-intestinal tract – to facilitate adequate consumption and utilization of dry dietary products to meet the nutritional requirements – which the consumption of milk provided, prior to weaning (Guilloteau et al., 2009). However, milk production in BBB ewes has been estimated to be low (less than 0.2 kg/day) at 100 days in milk, and this may not be a significant source of nutrients in lambs weaned after day 100 postpartum (Godfrey et al., 1997). Additionally, feed intake decreases immediately after weaning and then recovers (Poe et al., 1969). This tendency was greater in lambs weaned early, than those weaned later (8 weeks vs 12 weeks) (Abou Ward et al., 2008) and 4 weeks vs 8 weeks (Holcombe et al., 1994). This suggests feed intake to recover rapidly after weaning, and not be a limiting factor in lambs weaned early in life. Some evidence does however exist to support that continued suckling can reduce the rate of transition of the gastrointestinal tract (GIT) from the pre-ruminant to ruminant state. Thus allowing a greater proportion of starch to reach the small intestine, where digestion is more efficient than in the rumen. In contrast, weaning accelerates the development of the GIT and modifies the digestive secretions from a pre-ruminant to a ruminant state (Guilloteau et al., 2009). Thereby enhancing the efficiency of utilization of roughage diets. This may in part explain the better growth
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performance of unweaned lambs, when fed ˜ grain/concentrate diets (Caneque et al., 2001). Also, the better performance of weaned lambs placed on a post-weaning diet consisting only of roughage/pasture (Notter et al., 1991). The mortality rate of lambs was higher in early weaned, compared to late weaned lambs in Experiment 1, but not in Experiment 2. The mortality rate was highest in lambs weaned early in Experiment 1, and lowest in Experiment 2, when weaning occurred later (after 3.5 months in the early weaned group). High pre- and post-weaning mortality rates were also reported for hair sheep breeds in the tropics (Rastogi, 2001; Turkson and Sualisu, 2005). The findings in this study are consistent with those of Hatcher et al. (2010) who observed significantly higher mortalities in lambs that were lighter at weaning. These findings indicate that a significant loss in productivity may occur through increased lamb mortalities associated with the early weaning of lambs. To conclude, it can be said that the rearing of lambs with ewes prior to and during the breeding period did not negatively impact on the subsequent reproductive performance of the dams. Conversely, weaning BBB lambs increased the mortality rate of the lambs and resulted in an accelerated decline in lamb growth rates, regardless of the age at weaning. Management systems in which ewes are re-bred 2.5–3.5 months after lambing and lambs are reared continuously with ewes until market at 6.5–7.5 months of age may offer producers an opportunity to maximize the productivity of the ewes in terms of the kg of lamb marketed annually. Acknowledgements This research was supported by the Department of Food Production, University of the West Indies St. Augustine Sheep Project. The authors would like to thank Mr. Errol Fullerton and Darren Wong for their assistance in data collection and general management of the sheep flock. References Abou Ward, G.A., Tawila, M.A., Sawsan, M., Gad, A.A., El-Naggar, A., ElNaggar, S., 2008. Effect of weaning age on lamb’s performance. World J. Agric. Sci. 4, 569–573. Aksakal, V., Emsen, E., Ozdemir, M., Macit, M., 2009. Effects of various ages of weaning on growth performance of morkaraman lambs. J. Anim. Vet. Adv. 8, 1551–1554. Al-Trad, B., Wittek, T., Penner, G.B., Reisberg, K., Gäbel, G., Fürll, M., Aschenbach, J.R., 2010. Expression and activity of key hepatic gluconeogenesis enzymes in response to increasing intravenous infusions of glucose in dairy cows. J. Anim. Sci. 88, 2998–3008. ˜ V., Velasco, S., Díaz, M., Pérez, C., Huidobro, F., Lauzurica, S., ManCaneque, zanares, C., González, J., 2001. Effect of weaning age and slaughter weight on carcass and meat quality of Talaverana breed lambs raised at pasture. Anim. Sci. 73, 85–95.
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