Dietary Protein on Growth Performance, Serum Biochemical Index and offspring of Hu ewes in late pregnancy

The purpose of this study was to explore the effects of ewe growth performance, serum biochemical indicators and lamb growth and development at different protein levels in late pregnancy. A total of 15 pregnant ewes (46.4 ± 1.38kg initial BW) were assigned to 3 groups with 5 ewes in each group in a randomized block design. P1, P2 and P3 of three groups were fed diets with different levels of crude protein at 11.25%, 12.5% and 13.75% (low, medium and high) respectively, while the dietary energy levels remained unchanged. Choose ewes with the same body condition from 90 days of pregnancy to different protein diets during delivery, and feed the same diets during lactation. New-born lambs were left to suckle their dams freely for the first three days and were kept with their dams till weaning at 60 days of age. Dietary protein levels during late gestation showed no significant effect on the weight gain of ewes and their offspring in the late pregnancy (P > 0.05) but had significant effects on blood urea nitrogen (BUN), glucose (GLU), C-reactive protein (CRPL3) and ammonia nitrogen (NH3L) before parturition, and on triglyceride (TG) in lactating ewes. Dietary protein levels during late gestation had significant effects on birth height, body length, chest depth, chest circumference, straight crown hip length and curved crown hip length of lambs (P < 0.05) as well as on weaning body length, chest circumference, head width and head length (P < 0.05). The results showed that although different dietary protein levels during late gestation have no significant effects on growth performance of ewes, singleton, twins and triplets, it affects lambs’ body shape and ewes’ metabolism. Therefore, the optimum protein concentration for the growth of ewes and subsequent lambs in this experiment is 11.25%.


index, lamb body measurement
During the experiment, all the lambs and ewes were weighed individually in the 116 morning on an empty stomach. The ewes were weighed before the beginning of the 117 experiment and a week before parturition, and the lambs were weighed on the 0th day 118 after birth, then weighed every 10 days. The average daily gain (ADG) was calculated 119 on the basis of the average of 3 measurements for individual ADG (Yin et al., 2001). 120 The lamb's litter weight is the average weight of all lambs born to each ewe.

Blood biochemical indexes
122 Venous blood samples were taken from the neck of five ewes in each group at 140 123 days of pregnancy, 145 days of pregnancy, 1 day and 20 days after delivery before 124 morning feeding. Venous blood was taken from the neck of the lamb on the 60th day 125 of lactation and samples were collected with 5ml vacuum tube (Hunan Changsha Yiqun Table 3 shows that the initial weight, final weight, total gain and ADG did not have 161 a significant difference in the different protein levels of ewes (P > 0.05), but the ADG 162 in the low protein group was 28.14% and 32.79% higher than in the medium protein 163 group and high protein group. In Table 4, there was no significant difference in the 164 body weight of singletons, twins and triplets born by ewes at different protein levels (P 165 > 0.05). The litter birth weight, litter weight per 10 days and litter weight gain per 10 166 days in each group have been presented in Table 5. There was no significant difference 167 in litter birth weight, 10-day litter weight gain or 10-day litter weight among the three 168 groups (P > 0.05). In the birth weight of lambs there were no significant differences in 169 body weight and body weight gain per 10 days during lactation (P > 0.05; Table 6).

171
Dietary treatments with different protein levels showed significant differences in 172 BUN, GLU, CRPL3 and NH3L in ewes before delivery (P < 0.05; Table 7). Serum TG 173 content in the P2 group was significantly greater (P < 0.05, Table 8) than P1 and P3 174 groups. No significant difference in biochemical indexes of weaned lambs was 175 observed among the three groups (P＞0.05; Table 9). There were significant differences in body height, chest depth, chest circumference, 178 straight crown hip length and curved crown hip length among lambs in the born body 179 measurements (P < 0.05). The body height, chest depth and chest circumference of the 180 P1 group were significantly higher than those of P2 and P3 group, and the straight 181 crown hip length and curved crown hip length of the P3 group were significantly higher than those of the P1 and P2 groups (P < 0.05; Table 10).

183
For the weaning body size of lambs, significant differences were observed in body 184 length, chest circumference, head width and head length (P < 0.05). The size of the P3 185 group was significantly higher than that of the P1 and P2 groups (P < 0.05, Table 10).

187
The results of protein composition analysis of ewe milk in late pregnancy have been 188 shown in Table 11. Different protein levels had no significant effect on the milk fat rate, 189 milk protein rate, lactose rate, fat-free dry matter, total dry matter and urea nitrogen (P 190 > 0.05).

192
The change in body weight of ewes during pregnancy is an important index to assess 193 the effect of nutrition intake during pregnancy. When the nutrition received is 194 insufficient, the nutrients obtained by ewes will be used in the growth and development 195 of embryos, thus reducing the body weight gain of ewes. In this experiment, diets with 196 different protein levels had no effect on the growth performance of ewes, and the 197 postpartum weight of ewes was higher than that at 90 days of pregnancy, which 198 suggests that all the ewes were in good condition, and the diets met their requirements 199 for gestation and lactation. This implies that the diets supported foetal development and  and with the decrease of protein intake, the serum urea nitrogen content showed a decreasing trend, which was consistent with Preston (1965). The ammonia produced by 249 catabolism of various amino acids in various tissues of the body and the ammonia 250 absorbed by the intestinal canal enter the blood to form blood ammonia. In this 251 experiment, the NH3L content of ewes before delivery was higher than that before 252 weaning, while the NH3L content of the high-protein group before delivery was the 253 highest, indicating that the amino acid catabolism of high protein group was the fastest 254 before delivery and had the greatest effect on the growth and development of its 255 offspring lambs. CRPL3 is a kind of C-reactive protein, which is an indicator of 256 infection. CRPL3 was the highest in the high protein group before delivery; therefore, 257 low levels of protein should be used before delivery to avoid harm to ewes and lambs. why the blood glucose concentration during lactation is higher than that before giving 288 birth can be explained by the retention of glucose from gluconeogenesis after fat 289 mobilisation similar to the observations reported by Chilliard et al. (2000). This may 290 also explain why fat metabolism is affected. The concentration of TG during lactation 291 is lower than that during pregnancy, which may be due to the energy provided by TG catabolism for milk synthesis (Tanvi D. et al., 2016).

294
The protein levels of pregnant ewes ranged from 11.25% to 13.75%, which 295 significantly affected the body height, body length, chest depth, chest circumference, 296 straight crown hip length and curved crown hip length of the lamb at birth as well as 297 the body length, chest circumference, head width and head length in the weaning body 298 size of the lamb. The protein level of late pregnancy had no significant effect on the 299 production performance of lactating ewes, nor did it affect the nutritional composition 300 of milk and blood biochemical indexes of lambs, but there may be some effects on fat 301 metabolism of ewes. And it has no effect on the weight of singleton, twins and triplets.

302
Therefore, the optimum protein concentration for the growth of ewes and subsequent 303 lambs in this experiment is 11.25%. In production, the proper dietary protein level for 304 ewes during late gestation is beneficial in ensuring the development of Hu lambs.

306
There is no conflict of interest with respect to the current publication.