Performance and Measures of Stress in Lambs Weaned at 45 and 90 Days

 

Table 1 Weights and average daily gain (ADG) of lambs weaned at 45 and 90 d

SEM: standard error of the means.

 

Number of bleats was greatest in lambs weaned at an age of 45 d (P<0.05; Figure 1).

 

Figure 1 Differences between bleats / min (every 30 min between 0900 and 1200) before (d -1 to -2) and after weaning (d 0 to 3). Day 0 is when lambs were separated from their dams, completely

 

 

No vocalization occurred on the days before weaning. Animals weaned at an age of 45 d showed greater scores of agitation compared to animals weaned at an age of 90 d (P<0.05). All groups showed no agitation before weaning (Figure 2). Age of weaning affected blood cortisol, glucose and BUN concentration (P<0.01). Lambs weaned at 45 days had higher levels of the hormone and metabolites (Table 2). The age of bleeding affected cortisol concentration without any effects on glucose and BUN content. The serum level of cortisol was higher before weaning and decreased after weaning (Figure 3).

 

Table 2 Blood metabolites of lambs weaned at 45 and 90 d

SEM: standard error of the means.

 

The birth weights of lambs in both experimental groups were not different. This indicated that both of the groups were composed of animals with similar birth weight values at the beginning of the study. Weaning and 5-months weights were not different between groups. Among various early weaning studies, there were inconsistent results in lamb, kid and calf.

 

Figure 2 Agitation score (1=no agitation, 2=agitation and 3=high agitation) before (d -1 to -2) and after weaning (d 0 to 3). Day 0 is when lambs were separated from their dams, completely

 

 

Ugur et al. (2004) reported higher weaning weight in Sannan kids weaned at an age of 60 day rather than 45 day. However, those authors found no differences in the live weight of 3-and 4-month-old kids. Similar results were reported by Cañeque et al. (2001), who indicated lambs that remained with their dams displayed a better growth rate than early weaned lambs, in consequence of the longer period of milk consumption. However, in their study live weight at slaughter was the same for these two groups. In other hand, in agreement with our results, Winter (1985) weaned calves at 3, 5 and 7 weeks of age and reported no differences in average daily gain (ADG) and dry matter intake (DMI) pre and post-weaning. Other research showed calves weaned earlier were not different from calves weaned conventionally in feed intake, ADG and feed efficiency (Kehoe et al. 2006). In the study by Schichowski et al. (2008) lambs weaned at age of 8 week had greater ADG compare to lambs weaned at age of 16 week. Kuhn et al. (1990) stated that daily growth rate may be reduced by stress, because the release of glucocorticoid hormones is accompanied with reduced growth hormone production, which may lead to decreased feed intake. However, in our study ADG of early weaned lambs (45 d) was similar to lambs weaned at 90 d of age. This is somewhat surprising, since later weaned animals would have been expected to benefit from the additional milk received by the ewe. The availability of high quality concentrates may have allowed early weaned lambs to compensate for the loss of maternal milk by increased feed intake, resulting in a greater total intake of energy. In kids, Ugur et al. (2004) reported no significant differences between early weaned (45 d of age) and normal-age (60 d of age) weaned kids in ADG. Different management conditions in different farms could be the reason for variation in the live weight of the animals (Ugur et al. 2004). Zandi lambs can be successfully weaned at 45 days of age provided that they are accustomed to concentrate feed and roughage as early as possible.

 

Figure 3 The effect of sampling time on serum cortisol (ng/mL; day 0 is when lambs were completely separated from their dams)

 

 

 

As expected, results showed that younger weaned lambs had more stresswhen compared with older lambs based on the observed blood metabolites and behavioral parameters. Although in some studies plasma cortisol response to isolation was not affected by rearing conditions (Napolitano et al. 2002a; Napolitano et al. 2002b), other authors (Napolitano et al. 2003) observed a lower cortisol response in ewe-reared animals than in artificially reared lambs that were early weaned. Plasma cortisol response after separation from dam is related to age (Napolitano et al. 2008). Younger animals are still largely dependent on mothers and maternal separation can determine a higher cortisol response in these animals (Napolitano et al. 1995), whereas in older animals, a lower perception of stress may reduce differences between dam-suckled and early weaned lambs. High levels of glucose and BUN could be related to increasing of cortisol. Cortisol enables glucose availability which stimulates hepatic gluconeogenesis (Sherwood, 1995) and reduces glucose utilization (Gudev et al. 2007). Early weaned lambs bleating more than conventional weaned lambs. Increased vocalization rates in lambs occur after a stressor such as separation (Cockram et al. 1993). When lambs are, even temporarily, separated from mothers they show evident signs of stress represented by increased levels of bleating and locomotion (Alexander, 1977). The relationship between the ewe and its lambs disengages with age of the offspring and as the lambs become more autonomous (Orgeur et al. 1997). The intervals between suckling increase with age, indicating that 90-day-old lambs are more accustomed to a separation from the mother than younger lambs. With age, the distance between mother and young becomes longer. Older lambs also move more frequently and further from the ewe than younger lambs, and they do not vocalize as much as younger ones. Younger lambs show more activity and agitation, such as running around in the stable and searching for their dam.

 

CONCLUSION

Results of this study clearly demonstrate that lambs weaned at 45 days of age can be successfully weaned. However, lambs weaned at age of 90 day vocalized less and showed less behaviors indicative of agitation after separation compare with animals weaned at 45 day of age. Nevertheless, because detailed information on the possible benefits of alternative weaning procedures are lacking, further investigations on modified systems are needed.

 

ACKNOWLEDGEMENT

The authors would like to acknowledge the financial support of University of Tehran for this research.