THE COMBINED EFFECT OF SUCKLING SYSTEM AND WEANING WEIGHT ON MILK TRAITS OF NATIVE SHEEP

Data of the current stud, were collected on 32 Iraqi native sheep aged 2-5 years maintained on commercial flock. At lambing, the 32 ewes were divided into two equal groups, lambs in the 1 st group were left with their dams till weaning and then were milked twice daily till they dry off (Continuous), whereas the 2 nd group, lambs were separated at night for 12 hr. and the ewes were milked once daily at morning (Restricted). Then each main group was subdivided into two group to be weaned their lambs when they reached 3 or 4 times of their birth weight (WB1 and WB2). Results revealed that ewes of restricted suckling produced significantly (P < 0.05) more post weaning (80.80 vs.49.44 L), total milk yield (135.01 vs. 109.94 L) and sealable milk (99.86 vs. 49.44 L) and had significantly longer lactation period (169.3 vs. 140.2 days) compared ewes in continuous suckling. Also, results obtained indicate that daily gain in weight averaged 0.23 kg from birth to weaning and from birth to marketing and 0.24 kg from weaning to marketing and neither suckling system nor weaning weight affected these trait significantly. It can be concluded that restricted suckling resulted in an increase in sealable milk without any adverse effect on growth of lambs.


INTRODUCTION
In sheep, lactation is the most important function not only because the ewe remain an important dairy animal, but because efficient lactation is the foundation for good lamb performance necessary in any system of production (22). In most sheep's production system, the ewes rear their lambs, but there are great variation in the length of time that lambs are suckled. However, attempts to maximize commercial milk yield and/or lamb growth, a variety of weaning and rearing systems for ewes and their lambs have been carried out since late 1960's, and several mixed systems for early lactation management of ewes allowing both suckling and milking were also investigated (6,10,11,18,23,28). It has been also indicated that early weaning associated with restricted suckling gave higher marketable milk without causing a negative impact on the growth of lambs and thus provide economic benefits to the farmer (6,13,16,17,19).Since there is a lack of information on the effect of different suckling regime and weaning system on lactation performance and growth of lambs in native sheep, therefore, this study aimed to compare commercial milk during lactation and lamb growth traits under two different system of suckling and weaning weight in native Iraqi sheep.

MATERIALS AND METHODS
Data processed during the course of the current study, were collected on commercial sheep farm maintained at Duhok province, over the period 30 th November, 218 to 7 th June, 2019. Where a total of 32 native ewes aged 2-5 years and their single born lambs were used . Animals and management At 15-days post-lambing, the ewes were divided into two equal groups, lambs in the 1 th group were left with their dams till weaning except where milk was recorded at weekly interval and then were milked twice daily till they dry off (Continuous), whereas the 2 nd group, lambs were separated at night for 12 hr. and the ewes were milked once daily at morning till weaning and later twice daily till they dry off (Restricted). Then each main group was subdivided into two sub groups to be weaned their lambs when they reached 3 or 4 times of their birth weight (WB3 and WB4).All lambs were weighted at weekly interval till marketing.

Recording of milk:
Milk yield was calculated for both suckling system as follows: For pre-weaning in restricted suckling = Daily milk yield X 2 X 7 days For post-weaning in continuous and restricted suckling =Daily milk yield at morning + evening X 7 days Total milk yield in restricted suckling = preweaning + post-weaning Total milk yield in continuous suckling = postweaning milk yield only. Commercial milk yield: for restricted suckling = pre-weaning daily milk yield X7 days + post weaning milk yield Lactation period was calculated from lambing date up to dry off (less than 100/g), where as milking period was calculated for restricted suckling from lambing to dry off, and for continuous suckling from weaning to drying off.

Feeding
Following lambing, all ewes with their lambs were kept in the farm for a period of three days, after that the ewes and their lambs were allowed to graze natural pasture from 9:00 am to 5:00 pm.Fifteen days post lambing, a concentrate mixture (15% crude protein and 2790 kcal/kg) was offered to ewes according to NRC (20) requirement.

Statistical analysis
General Linear model was used to estimate Best Linear unbiased effects of treatments on studied traits (SAS, 27). Duncan multiple range test (7) was used to test the differences between the sub classes of each factor. Since the interaction of all studied traits was not significant, therefore the interaction was excluded from the results.

RESULTS AND DISCUSSION
Results revealed that the overall means of preweaning, post-weaning, total, and commercial milk yield averaged 57.25 ± 3.22, 65.66 ± 6.63, 122.91 ±7.56 and 75.52 ± 7.72 L, respectively. Moreover, total milk yield recorded herein by native ewes is higher than those reported earlier for the Awassi in Iraq (3, 14) as well as it is higher than those recorded earlier for karadi ewes (2,4,21).However, such value is very close to those found earthier for Awassi ewes ( 126.05 L) and karadi ewes (126.39 L) by Alkass and Akreyi (1). Such differences in yield could be attributed to the genetic make-up of the animals, as well as conditions of ewes and feeding and management practices followed in different farms. It appears from Table 1 (6). This result demonstrate that the early lactation management of native ewes has a great impact on overall lactation performance. This finding showed that more commercial milk (50.64%) could be obtained when ewes will be milked once daily in addition to suckling up to weaning compared to ewes that will be only suckled their lambs during this period. Therefore, commercial milk yield of ewes can be increased by the application of restricted suckling system. Results presented in Table 1 revealed that ewes of BW4 produced significantly (p < 0.05) more milk (66.79 L) than do ewes in BW3 group (48.34 L) during pre-weaning period. This finding is obvious because lambs of BW3 reached their target weight at a shorter period (45.13 days) than those of BW4 (58.86 days). However, no significant differences between BW3 and BW4 exist in post-weaning, total and commercial milk yield. Similarly, working on Saanen and Alpine goats, Gokdalet al. (12) concluded that kids weaned at 3 times their individual birth weight yielded more milk (483.74 L) as compared with kids weaned when they reached four times of their birth weight (427.05 L). In the present investigation, it seems from Table 1 that the two systems of production yielded almost similar amount of milk at peak (776.42 vs. 773.66 ml) as well as when they attained their peak of production at a same time (38.71 vs. 39.20 days). Moreover, the PMY recorded herein is higher than the values obtained by Alkass and Akreyi. (1) for Awassi (617.33ml) and for karadi ewes ewes (626.56 ml), but it is lower than the amount (1.467 L) obtained by Merkhan (19) for the Awassi raised in another commercial farm. Such differences may be attributed to the differences in genetic make-up and different management and feeding system followed in each farm. Also, Mckusicket al. (18) found that greater peak milk yield was attained by ewes suckle their lambs for 9 hr in the morning and machine milked (2.93 kg) than ewes exclusively suckled by their lambs (2.56 kg) or ewes machine milked twice daily (2.81 kg). Lactation period averaged 169.33 and 140.28 days for ewes maintained in restricted and continuous suckling system, respectively; and the difference between them is significant (p < 0.05) ( Table 1). The length of lactation recorded herein is longer than that reported earlier by other workers on Awassi ewes (3, 9,14,19) as well as for karadi ewes (2), but it is almost similar to those indicated by Alkass and A keryi. (1) for Awassi (169.66 daya) and karadi ewes (168.71 days). The significant difference between the two suckling regime could be due to the act of suckling and milking rather than suckling only in continuous suckling group, so the ewes are more persist to milking for a longer period. It seems from Table 1 that ewes in continuous suckling group had significantly (p < 0.05) a shorter milking period (86.50 days) than did the ewes in restricted suckling ewes (169.33 days), because the ewes kept in continuous suckling were not milked during weaning period. Similar results have been reported by Dikmenet al. (6). With the regard to differences of weaning weight, it seems that lactation period and milking period are almost similar in both BW3 and BW4.

Growth rate of lambs
In the current investigation, the overall mean of weights at birth, weaning and marketing weights averaged 4.57 ± 0.14, 16.13 ± 0.35 and 28.95 ± 0.83 kg, respectively. Also, the daily gain in weight from birth to weaning, birth to marketing and weaning to marketing averaged respectively, 0.23 ± 0.01, 0.23 ± 0.01 and 0.24 ± 0.01. (Table 2).The average daily gain (0.23 ± 0.01 kg) attained in the present investigation is higher than those reported earlier for Awassi sheep in Iraq by Eliya and Juma (9), by Kazzal (15) Table 2. The effect of suckling system and weaning weight on growth rate of lambs (kg).