Feed Intake, Nutrient Digestion, Growth and Reproductive Performances of Boran-Friesian Cross Breed Dairy Heifers Through Different Wheat Straw to Concentrate Feeds

: This study was conducted to examine the effect of different wheat straw and concentrate proportions on feed intake, nutrient digestibility, growth and reproductive performances of F1 cross breed (Boran X Friesian) dairy heifers. Wheat straw (WS) with 93% dry matter content was chopped (3-5 cm in length) and mixed with concentrate, molasses and water. The amount of water used for the preparation of total mixed ration was three fold of the molasses amount. Twelve dairy heifers (90.45 ± 7.37 kg LW, mean ±S.D) were randomly assigned to one of the three dietary treatments (WS80= 80% WS: 20% concentrate; WS60 = 60% WS: 40% concentrate) and WS40 = (40% WS: 60% concentrate) in a completely randomized block design. The diets were offered ad-libitum and allowing 15-20% refusal. The experiment was consisted of 345 days of feeding trial and 7 days for the measurement of digestibility. Different wheat straw and concentrate proportion had no significant effect on organic matter intake of dairy heifers. In contrast, dry matter (DM), crude protein (CP) and acid detergent fiber (ADF) and neutral detergent fiber (NDF) intakes were greater when the heifers were fed WS40 versus the other treatments. The greater (P<0.001) DM, CP, ADF and NDF digestibility, feed conversion efficiency and growth rate were observed in WS40 than the other treatments. The greater (P<0.001) body weight at first service for dairy heifers was perceived in WS80 than the other dietary treatments. Conversely, the smallest age at first service, age at first conception and number of service per conception for dairy heifers was noticed in WS40 than the other dietary treatments. Raising dairy heifers by using 40% wheat straw and 60% concentrate can be recommended for practical application.


Introduction
Well-grown heifers are the best foundation stock of a dairy herd.But in many farms, heifers become the most neglected group which leads to a poor growth rate and age at first calving greater than 24 months.The main objective of heifer rearing program is to achieve appropriate body weight (220kg in Jersey breed) at the breeding age and attaining 1 st calving at 24 month of age [8].The use of TMR for young heifers may result in a better balance of nutrient intake by avoiding individual preferences for forage or concentrates.It was found that heifers fed TMR from a young age were able to distribute their feeding activity more evenly throughout the day and compete less for feed than heifers fed a top-dressed ration [4].The objective of this study was to examine the influence of different proportion of wheat straw to concentrate based total mixed ration on feed intake, nutrient digestibility, growth and reproductive performance of crossbred dairy heifers.

Description of the Study Area
The study was carried out at Holeta Agricultural Research Centre, Ethiopia.The center is located at 9°03'28.82"E latitude and 38°30'17.59"E longitude at an elevation of 2,400 m above sea level.The mean annual temperature and rainfall during the study year (2020) were 18°C and 1225 mm, respectively.

Experimental Design
Twelve post weaned F1 Boran-Friesian Cross Breed diary heifers (90.45 ± 7.37 kg and 95±12 days, mean ±S.D, live body weight and age, respectively) were randomly assigned in a completely randomized block design.Heifers were drenched with broad-spectrum anti-helminthic (Albendazole 2500 mg) prior to the commencement of the feeding trial.The heifers were kept in individual pens.Wheat straw (WS) with 93% of dry matter content was chopped by using on-farm hammer mill.A tractor was used as energy sources of chopping wheat straw with a standard size of 2-5 cm.During the chopping process the amount of benzene consumed by the tractor per kg of chopped wheat straw was 2 litters.After the operation of chopping the wheat straw was mixed with concentrate and molasses.Water was also used for the preparation of total mixed ration.The amount of water used for the preparation of TMR was 3 fold of the molasses amount.The three dietary treatments used for 345 days feeding trial were: -WS80 (80% wheat straw: 20% concentrate); WS60 (60% wheat straw: 40% concentrate) and WS40 (40% wheat straw: 60% concentrate).The TMR diets were offered ad-libitum and allowing 15-20% refusal.

Digestibility Trial
At the end of the experiment, faces from each heifer were collected for seven days.Feed and fecal samples were analyzed by the methods of [1,13].In vitro organic matter digestibility was determined by [12] methods.

Statistical Analysis
The data were subjected to analysis SAS procedure [11].Tukey means separation test at 5% level of significance was used.
The model was: Where, Y ij is the observation on i th treatment in j th block; µ is overall mean; T i (i=1, 2, 3) is the effect of i th treatment; B i (i=1, 2, 3) is the effect of i th block; E ij = Random error (residuals)

Chemical Composition of Feed
The chemical composition of the feed is presented in Table 2.Among supplemental feed ingredients and the concentrate mix, the two protein source feeds (Cotton seed cake &Noug seed cake noted to have the highest CP and the lowest digestible organic matter compared to the energy source feed (wheat bran).Noug seed cake was found to be rich in its ash and permanent lignin contents than the remaining protein and energy supplemental feeds.Greater variations of nutrients were observed the TMR diets.The mean CP and Invitro organic matter digestibility contents of concentrate feeds in the present study are comparable with the report of [6].

Feed Intake
The different proportion of wheat straw and concentrates based total mixed rations had no negative impacts on organic matter intake but dry matter, fiber fractions (ADF and NDF) were greater (P<0.05) at WS60 than the other dietary treatments (Table 3).The average daily dry matter and crude protein intakes for the dairy heifers consuming 80, 60, and 40% wheat straw based rations was 6.91, 7.03 and 7.38 kg, and 640, 860 and 960 gram, respectively.The average dry matter intake and bypass' protein derived from the two protein source feeds (Noug seed cake and cottonseed cake) were greater (P<0.01) when there was a high proportion of concentrates in the ration.This finding is consistent with the proportion of chopped maize stover silage increased in the diet of dairy heifers which leads to depress the intake of dry matter, fiber fractions (NDF and NDF) and nutrient digestibility [5].

Apparent Digestibility
Digestibility coefficients were reduced as wheat straw replaced with concentrate feed (Table 4).The greater (P<0.001)apparent digestibility coefficients of dry matter, organic matter, crude protein and fiber fractions (ADF and NDF) were observed in WS40 than the other treatments.The average dry matter digestibility of the dairy heifers consuming 80, 60, and 40% wheat straw rations was 55.21, 64.32 and 69.97%, respectively.The coefficients of apparent digestibility for dry matter, organic matter and crude protein, acid detergent fiber and neutral detergent fiber values, increased as the proportion of concentrate in the ration increased [10].In the present study, dairy heifers fed the WS40 diet, which was the highest coefficients of apparent digestibility for dry matter, organic matter and crude protein, acid detergent fiber and neutral detergent fiber values compared with dairy heifers fed the other dietary treatments which is consistency with the finding of [5,8] who found that the higher coefficients of apparent digestibility for dry matter, organic matter and crude protein, acid detergent fiber and neutral detergent fiber values, as the proportion of concentrate in the maize stover silage based total mixed ration was increased.In contrast with this finding, the digestibility coefficient for crude fiber decreased as the proportion of concentrate in the ration became greater [10].

Growth and Feed Conversion
Daily body weight gain, protein and feed conversion of the dairy heifers were depressed with linear trends wheat straw replaced protein-rich concentrate in the diet (Table 5).The higher (P<0.001)daily body weight gain, feed and protein conversion efficiency of dairy heifers was observed in 40% chopped wheat straw and 60% concentrate based total mixed ration compared to the other dietary treatments.The average daily dry matter and crude protein intake for the dairy heifers consuming 80, 60, and 40% wheat straw rations was 6.91, 7.03 and 7.38 kg, and 640, 860 and 960 gr, respectively.As the proportion of the concentrate feed in the treatment diet increased from 20% to 60% daily growth rate was increased by 170g.Several possible explanations exist for the higher daily growth rate of dairy heifers which were fed WS40.First, it may be due, in part, to the 22% dry matter and crude protein apparent digestibility increment which are important to daily body weight gain.Second, the mainly to the increment of protein from Noug seed cake and cottonseed meal that are known to have characteristics that favor protein escape from the rumen and hence more Noug seed cake available to the animal.There was a high relationship between the average daily body weight gain and feed conversion efficiency with bypass protein intake (r ~ +0.98 and +0.99, respectively, figure 1 and figure 2).This finding is consistent with the finding of [5] who found that the daily body weight gain and feed conversion efficiency for dairy heifers is higher as the proportion of concentrate in the maize stover based total mixed ration became greater.

Reproductive Performance
The weight at first service, age at first service, age at first conception and number of service per conception for the dairy heifers is presented in (Table 6).The average weight and age at first of the dairy heifers consuming 80, 60, and 40% wheat straw rations was 254.01, 248.20 and 236.66 kg, and 17.53, 15.91 and 13.23 months, respectively.The greater (P<0.001)body weight at first service for dairy heifers was observed in WS80 than the other dietary treatments.Conversely, the smallest age at first service, age at first conception and number of service per conception for dairy heifers was observed in WS40 than the other dietary treatments.Several possible reasons are exist for the improvement of dairy heifers reproductive performances such as age at first service, age at first conception and number of service per conception First, it may be due, in part, to the higher bypass protein intake, the 22% dry matter and crude protein apparent digestibility increment in the treatment diet.Secondly, the reproductive performances of dairy heifers were improved due to the greater amount of concentrate in ration, feed conversion efficiency and daily growth rate in WS40 treatment diet became greater.There was a linear negative relationship between the age at first conception and bypass protein intake (r ~ 0.99, respectively, figure 3).In the case of total mixed ration, energy and protein utilization in the rumen was improved and helped to facilitate productive performances of the animals as reported by [9].The higher weight at first service in TMR feeding in the present study is in agreement with the result of [7] who found the higher weight at first service in a short period for dairy heifers fed that higher concentrate to roughage feeds.Number of insemination per conception in TMR feeding observed in the present study is contrary with the finding of [4] who found no effect of TMR on insemination per conception of dairy cows while the current finding was consistent with the report of [2,3] who found that the higher concentrate feed in the ration has positive effects on service per conception.Relationship between age at fist conception and intake of "bypass" protein derived from Noug cake and cottonseed cake.

Conclusions
It is proposed that the reduction in growth performance was partly due to the 22% decrease in DM and CP digestibility but mainly to the due to reduction in protein from Noug cake and cottonseed cakes that are known to have characterizes that four the escape from the rumen., the smallest age at first service, age at first conception and number of service per conception for dairy heifers was perceived in 40% wheat straw.Raising o dairy heifers by using 40% wheat straw and 60% concentrate can be recommended for practical application.

Figure 1 .
Figure 1.Relationship between growth rate and intake of "bypass" protein derived from Noug cake and cottonseed cake.

Figure 2 .
Figure 2. Relationship between feed conversion and intake of "bypass" protein derived from Noug and cottonseed cake.

Figure 3 .
Figure 3. Relationship between age at fist conception and intake of "bypass"protein derived from Noug cake and cottonseed cake.

Table 1 .
Feed ingredients in the total mixed rations (DM basis).

Table 4 .
Dry matter and nutrient digestibility coefficients of the dietary treatments.

Table 5 .
Growth performance of dairy heifers.

Table 6 .
Performance (Mean ± SE) of heifers' fed total mixed ration and conventional feed.