Response to Partial Replacement of Yellow Corn with Sub-Graded Sweet Potato Tuber as a Non-Traditional Source of Energy on the Productive and Reproductive Performance of Dairy Cows.
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Abstract
Twenty crossbreed Friesian cows (4-5 years old), in the 2nd and 3rd season of their early lactation stage with an average live body weight of 520 kg were divided into 4 experimental groups using two way classification design. The first group was fed ration containing concentrate feed mixture (CFM), yellow corn, berseem hay and rice straw, while The 2nd, 3rd and 4th groups were fed ration where 33, 66 and 100 % yellow corn (YC) was replaced by sub-graded sweet potato tubers (SPT) on DM basis, respectively.
No significant differences were detected between treatments for nutrients digestibility of DM, OM, CF, EE, NFE and energy digestibility. Groups that fed control and 33 % SPT were (P < 0.05) higher in apparent digestibility of NDF, ADF and cellulose compared with groups fed 66 and 100 % SPT. While no significant differences were observed among groups in digestibility of ADL and hemi-cellulose. Feeding values as TDN were not significant between treatments. But the DCP was significantly (P<0.05) lower with increasing level of SPT in the rations.
No significant differences were detected between treatments for total milk yield, fat, protein, total solids, solids not fat (SNF) and lactose contents with replacement SPT instead of YC. FCM, SNF and lactose yield were increased significantly (P< 0.05) with T1 (100 % YC) compared with T4 (100 % SPT), but T2 and T3 were not significant. Protein and TS yield were decreased significantly (P<0.05) with T3 and T4 compared to T1.
Feeding SPT at different levels as replacement of YC had no significant effects on serum total protein (TP), albumin, globulin, A/G ratio, ALT and AST. Animals fed SPT had significantly (P<0.05) lower serum urea-N concentration than those fed YC. No significant differences for days of first estrus were observed among the treatments. The intervals between calving to first behavioral estrous were 48.9, 46.26, 47.65 and 49.11 days in cows that fed rations containing 100 % YC, 33 % SPT, 66 % SPT and 100 % SPT, respectively. The days from calving to the first insemination did not significantly differ among all groups of treated cows. The number of inseminations per conception was not significantly affected by replacement SPT instead of YC as source of energy. The pregnancy rate measured at the end of the treatment period, the values were 90.50, 90.50, 88.66 and 88.33 % for T1, T2, T3 and T4, respectively. Conception rate following the first postpartum AI was 66.26, 50.50, 56.33 and 66.33 for cows received ration containing 100 % YC, 33 % SPT, 66 % SPT and 100 % SPT, respectively. During the cycle, the plasma progesterone values of the cows fed ration containing SPT instead YC were lower, the values were insignificant.
Higher dietary level of SPT as a replacement of corn did not affect total DMI. DMI (Kg)/milk (Kg) was increased (p<0.05) significantly with higher level of SPT (T4) compared with control ones, while TDN (Kg)/milk (Kg) and DCP (g)/milk (Kg) were did not affect with T2 and T4. Feeding cost of produce Kg milk was reduced by 7.46, 11.94 and 22.39% for T2, T3 and T4, respectively, compared with control one.
It is recommended that using sub-graded SPT as a source of energy and protein at harvesting season of sweet potato in dairy cows rations at first lactation period instead of corn grain would improve the revenue of dairy cows.