Assessment on reproductive performance of crossbred dairy cows selected as recipient for embryo transfer in urban set up bishoftu, Central Ethiopia

Ethiopia is a home for many livestock species and suitable for livestock production owning the largest livestock population in Africa, which has been estimated at 54 million heads of cattle, 25.5 million sheep, and 24.06 million goats. From the total cattle population, indigenous breeds are accounted for about 99.2%, while the hybrids and highly productive exotic breeds were represented by only 0.64% and 0.1%, respectively. Livestock production is one of the fastest-growing agricultural subsectors in developing countries, where it accounts for more than a third of the agricultural gross domestic product (GDP). Livestock production is expected to grow tremendously in line with the projected demand for animal products. Therefore, the methods of livestock production must change to allow for effi ciency and improvement in productivity [1,2].


Introduction
Ethiopia is a home for many livestock species and suitable for livestock production owning the largest livestock population in Africa, which has been estimated at 54 million heads of cattle, 25.5 million sheep, and 24.06 million goats. From the total cattle population, indigenous breeds are accounted for about 99.2%, while the hybrids and highly productive exotic breeds were represented by only 0.64% and 0.1%, respectively.
Livestock production is one of the fastest-growing agricultural subsectors in developing countries, where it accounts for more than a third of the agricultural gross domestic product (GDP).
Livestock production is expected to grow tremendously in line with the projected demand for animal products. Therefore, the methods of livestock production must change to allow for effi ciency and improvement in productivity [1,2].
Cattle contribute to about 83 % of the total volume of milk produced in Ethiopia followed by goats and camels. Estimates indicated that about 97% of the country's total annual milk production is contributed by indigenous breeds [3]. Despite the huge livestock population the country holds, the per capita consumption of milk is estimated to be only 20 kg/year

Abstract
The reproductive status of a recipient cow is among the factors that infl uence the success of embryo transfer in bovine. The study was carried out on a total of 276 cows from 25 dairy farms classifi ed as large (>20 cows), medium (10-20 cows) and small scale (1-10 cows) dairy production system. Data were collected through personal interviews of owners, from an individual animal record and gynecological evaluation of animals. Accordingly, the overall mean (±SD) of AFC, CI, LL, DMY, and NSPC were 30.07±2.17 months, 13.33±2.84 months, 9.08±1.10 months, 14.33±4.59 liters/day and 1.59±1.02, respectively. Milk yield and body condition did not have a signifi cant effect on NSPC (P > 0.05) whereas parity signifi cantly infl uenced NSPC, with cows in parity 3 showing the lowest NSPC (p<0.05). Farm size signifi cantly infl uenced AFC, NSPC, and DMY (p<0.05). Milk yield was highly associated with increasing parity number. There was no statistically signifi cant difference in NSPC between the breeding method (AI and NS) (P > 0.05). In conclusion, most of the reproductive parameters of the present population were within the range, however, some of the reproductive indices tended to be infl uenced by the scale of production. Findings of this study highlight that the selection of embryo recipient cows in the small and medium-sized farms should be meticulous considering the important indices particularly NSPC. Besides, feeding management, as shown by the body condition has been another parameter requiring consideration, particularly in small scale production.

Research Article
Assessment on reproductive performance of crossbred dairy cows selected as recipient for embryo transfer in urban set up bishoftu, Central Ethiopia as compared to 27 kg for other African countries and 100kg for the world [4]. Considering the important prospective for smallholder income generation and employment opportunities from the high-value dairy products, the development of the dairy sector can contribute immensely to poverty alleviation and improved nutrition in the country [5].
Reproduction is the backbone of animal production and productivity is the key to development. Reproductive ineffi ciency is one of the most important causes of economic losses in animal industries and it is realized throughout the world. Despite the remarkable advancement that has been made in the fi eld of reproductive physiology in recent years, infertility due to low conception rate and high embryonic mortality rate remains a major problem [6,7]. To meet future needs and to be able to sustain agricultural production, agricultural research and its applications need to use all emerging technologies one of which is modern reproductive biotechnologies. Thus, various assisted-reproductive techniques have been developed and refi ed to obtain a large number of offspring from genetically superior animals or obtain offspring from infertile (or subfertile) animals in addition to disease control [8,9].
The reproductive performance of the breeding female is probably the single most important factor that is a prerequisite for a sustainable dairy production system and infl uencing productivity. Especially, the economics of dairy enterprise is based on the effi cient reproductive performance of dairy animals [2,10]. The most common indices of reproductive performance are age at the fi rst service, age at fi rst calving, calving interval, number of services per conception, and breeding effi ciency. Maximum rates of breeding effi ciency in dairy cattle are attained through regular calving of one viable offspring per breeding cow in the herd in a year. Lowered breeding effi ciency rates can be due to the long calving interval of a dairy cow which is mainly due either to low conception rate and/or high early embryonic mortality [11].
Poor reproductive performance results in excessively late age at fi rst calving and long lactations. Both are costly to the dairy producers because of the veterinarian breeding expense, high reproductive replacement costs, and fewer calves being born [12]. Low reproductive effi ciency due either to delayed fi rst service, missed estrus, or multiple services per-conception continues to be a major problem in dairy herds. Several reports have indicated that poor reproductive performance, manifested as prolonged calving intervals, can result in reduced milk yield and increased culling rates and replacement cost. Such animals are not suitable for application reproductive biotechnology [13].
Reproductive biotechnologies intend to be used routinely to shorten generational intervals and to propagate genetic material among breeding animal populations. To achieve this goal, reproductive technologies have been developed in generations over the years, namely artifi ial insemination (AI), embryo transfer (ET), manipulation of fertilization in vitro (IVF), cloning and transgenesis [9,14]. These, together with sperm separation techniques, including that of selection of spermatozoa for chromosomal sex (commonly named sex-sorting) all face today a strong wave of increasing commercialization [15].
Bovine embryo transfer technology involves the selection and management, both physical and pharmacological, of donor and recipient animals, and the collection and transfer of embryos within a narrow window of time following estrus.
Ideally, the transfer of embryos in the cow will result in a high pregnancy rate provided that estrus in the donor and recipient occurred within 24 hr of each other. This requires the cycling of each recipient and good reproductive performance, which in turn is infl uenced by various management factors, to successfully result in a live offspring at the end of the embryo transfer. This technology has been incorporated into large dairy and beef cattle operations and often requires the participation of herd veterinarians. Embryo transfer is one step in the process of removing one or more embryos from the reproductive tract of a donor female and transferring them to one or more recipient females [2,16].
Recipient selection is one of the fi rst objectives for an embryo transfer program to achieve. Although heifers used as recipients are common practice in many places, it does come with its perils. These animals typically will give higher pregnancy rates than cows, ranging from 10% to 23%. The downside is that this animal is used to carry genetics that typically is not selected for calving ease. Calving management has to be a primary concern when using heifers as recipients.
Advanced parity dairy cows from 3 to 8 years of age are the optimum recipients with better milk production, better reproductive history, and better colostrum which can be selected for disposition [17].
Several types of research have been conducted to evaluate the reproductive performance of crossbreds especially for different exotic blood levels crossbred of dairy cows under a relatively controlled condition at research centers, government-owned farms [18]. However, few indicate that these animals are suitable for the application of MOET. Thus, the study was conducted to assess and compare the reproductive performance of crossbred recipient dairy cows selected for embryo transfer based on the scale of the production system and selected parameter.

Study area
The study was conducted in the Oromia regional state in Bishoftu town from December 2016 to May 2017. Bishoftu is located 45 km southeast of the capital city Addis Ababa in the Ethiopian highlands ( Figure 1). The area is located at 9 0 N latitude and 40 0 E longitudes. The altitude is about 1880meters above sea level. The average annual rainfall is 866 mm with a bimodal distribution. The long rainy season extends from June to September (of which 84% of the rain is expected) followed by a dry season from October to February. The short rainy season lasts from March to May. The mean annual minimum and maximum temperatures are 14ºC and 26ºC, respectively.
The humidity of the study area is 66% in summer and 56% in winter [1,19].

Study animals
This study was conducted on crossbred dairy cows belonging to large (≥20 cows), medium (11)(12)(13)(14)(15)(16)(17)(18)(19)(20), and small farms (≤10) owned by dairy farmers in Bishoftu town. The majority of dairy producers in the town are market-oriented smallholder dairy farmers which are organized under one dairy cooperative called, Ada'a milk and milk products marketing cooperative share company. There are also few governmental and privately owned large (commercial) scale dairy farms with a milking herd size of over 50.
Feeding basically constituted hay, straw, and concentrate mainly from spent grain, silage, and poultry manure. Water was given ad libitum in all farms. Vaccination is practiced in medium and large farms for common diseases including FMD and Anthrax, Blackleg, Contagious Bovine Pleuropneumonia, Pasteurellosis, Lumpy skin disease. Breeding in all farms was using either natural or artifi cial insemination mostly from bulls of exotic blood. Housing conditions were mostly similar among all dairy farms with concrete fl oor and tie-stall system. Some of the larger farms have either a waste disposal system or produce biogas.

Study design and methodology
All the dairy owners were invited for a day workshop for discussion on the application and benefi t of assisted reproductive technology particularly Multiple Ovulation and Embryo Transfer (MOET). They were explained on the MOET procedure, what constituted a recipient population, and their consent or willingness to participate in the project for embryo transfer to allow their animals as recipients were considered during the selection of the farms. Subsequently, a crosssectional study and retrospective data analysis were conducted to study the reproductive performance of crossbred recipient dairy cows selected for the MOET program in an urban setup.

Sample size determination
The selection of the farms was purposive based on he rd location, use of AI for breeding, presence of proper housing, fulfi lling minimum hygienic requirements, and presence of a of dairy cows (sample size) was determined according to the formula given by Arsham [20], as per the formula:

N=0.25/SE 2
Where N= Sample size, SE= Standard error Therefore, using standard error of 3% with a 95% confi dence level a total of 276 animals were selected for the study.

Method of data collection
All animals included in this study were registered in a data collection sheet based on their Identifi cation number (ID) which is written on their ear tags, those animals which do not have ear tags their name was used as identity number. Data were collected through personal interviews and recorded data.
All information about individual cows such as age, parity, age  to the method described in Garnsworthy and Pryce, et al. [21,22].

The overall reproductive performance of selected crossbred dairy cows
According to the current assessment, Feeding mainly constituted roughage (100%), concentrate (62.4%), poultry manure (20.9%), and silage (5.4%). Feeding a concentrate have signifi cantly (p<0.05) infl uence age at fi rst calving (AFC) The mean age for those feeding concentrates was 30.01±2.11 months and for those not feeding 31.2±2.80 months.
The descriptive statistics of age, BCS, hygiene score, and reproductive performance for the different farm sizes were given in (Table 1).  Table 2.

Association of milk yield and lactation length with parity number
As indicated in Figure 2, the milk yield of the cross-bred dairy cows was increased as the number of parity increases.
Thus, the milk yield was highly associated with increasing parity. Moreover, the number of farm size signifi cantly infl uenced AFC, NSPC, and DMY (p<0.05). However, the lactation length of the cross-bred dairy cows remains constant even though the num ber of parity increases (Figure 3).

The effect of mating system on the number of services per conception
Furthermore, in the current study, the association of different mating systems with the number of services per conception and its effect on the reproductive performance of the selected cross-bred dairy cows. There was no statistically signifi cant difference in NSPC between the breeding method (AI and NS) (P > 0.05). The mean value of NSPC under artifi cial insemination (AI), natural service (NS), and both were shown in Table 3.

Discussion
In the present study, assessment on the reproductive performance of crossbred dairy cows selected as a recipient for embryo transfer in an urban setup in Bishoftu town was conducted on 276 cows from 25 dairy farms. Out of the total farms, the mean AFC for large scale was 28.39±2.6 months and this was lower than the previous fi nding of Lemma and Kebede,[23] Dinka, [24] and Mureda and Zeleke, [25] who also reported between 32, 34.2 and 36.2 months for crossbred cows in different parts of Ethiopia, respectively. Other authors also indicate 58.3-36.8 months for crossbred dairy heifer at two locations in smallholder dairy farms in Zimbabwe [26] and 43.2-53.6 months for different crossbreeds in Sudan [27].
On the other hand, an analysis of over one million records indicated AFC for Holstein-Friesian heifers to be 28.1 months (Pirlo, et al. 2000). The mean (±SD) of age at fi rst calving for large scale farms was lower than for crossbreds dairy cows reported in Ethiopia [28][29][30]. In the present study, the AFC in medium-scale farms was 30.35±2.24 month and this was lower than the previous report of Wassie, et al. [30] in Bale zone of Oromia Regional State, Ethiopia (41.16±0.56 months) and Masama, et al. [26] in crossbred dairy heifers in Zimbabwe (58.3 months).
In the current study, the mean ±SD of age at fi rst calving for small scale farms was 32.68±1.9 months. The current fi nding is comparable with 34.8±4 months which is reported by Dinka [24] in crossbred dairy cows in Asella and Nibret [31] in Gondar which report 32.4 months and 31.9±0.22 months, which is reported by Yifat [32] for crossbreed in Zway. The Present results were lower than the previous report of Tassew and Seifu, [33] that reports 36 months, Mureda and Zeleke [25] who reports 36.2 months and Kumar et al., [34] in Mekelle which report 36.4±17 months. However, the mean AFC in this study is higher than 26.9±5.4 months reported by Genzebu, et al. [35] for smallholder crossbred dairy cows in Bishoftu town.
The difference between the current study and previous report might be due to environmental conditions and husbandry practices which may affect body growth. These may retard growth rate, delay puberty, reduced fertility, and conception. Farm size has been indicated to signifi cantly affect AFC in dairy animals [36]. Unlike farms using AI, farms using Natural service have a better chance of detecting estrus and getting heifers or cows pregnant at the fi rst opportunity. Farms using AI have to go through the diffi culties of estrus detection required for proper insemination which is both the number one problem in the success of AI in Ethiopia.
In this study, the mean calving Interval (CI) of the selected dairy cows was 13.33±2.84 months. A report of 13.6 months CI by Yifat, et al. [32]  In the present study, the number of services per conception (NSPC) was 1.59±1.02 months. This was comparable with previous studies reported for tropical conditions for crossbred cows by Rahman, et al. [40] and the central highlands of Ethiopia by Shiferaw, et al. [18]. However, it was lower than   , who also reported that AFC was shorter in heifers fed concentrate than those fed fodder only. The infl uence of feeding on growth rate has been a fact in the dairy animals. Replacement heifers have to be fed in such a way that they attain at least 60% of their adult size by the time they reach puberty and 80% of their adult size by the time they calve for the fi rst time. Parity also affected NSPC, with parity 3 showing the lowest NSPC. This is comparable to the previous report Mureda and Zeleke [29], who found that parity signifi cantly infl uenced NSPC in Holstein Friesian x Zebu cross dairy cows kept in different production systems in Eastern lowland of Ethiopia.

Con clusion and recommendations
The current study population exhibited a moderate fi nding of reproductive performance indices which could be suitable as a fi rst-line screening for the recipient population.
Accordingly, AFC, CI, and NSPC were the most important indices of reproductive performance. Lowered breeding effi ciency rates can be due to the long calving interval of a dairy cow which is mainly due either to low conception rate and/or high early embryonic mortality. The reproductive performance traits were comparatively good within large scale production and followed by medium and small-scale dairy production systems. The management condition in small-scale production has infl uenced the overall performance. Hence, selection recipient cows from such farms require meticulous consideration reproductive indices. In conclusion, the improvement in the reproductive and productive performance of dairy cows by improving the feeding system of the dairy cows. Also, attention should be given to heat detection, health care, timely insemination. Standard record-keeping practice on reproductive and productive traits should be established.
Furthermore, the follow up of reproductive performance on dairy cows in the small-scale production is required.=