EFFECT OF NON-GENETIC FACTORS ON PRODUCTIVE AND REPRODUCTIVE PERFORMANCE IN CROSSBRED COWS MAINTAINED AT LIVESTOCK EXPERIMENT STATION, QADIRABAD DISTRICT SAHIWAL

: The present study was undertaken to evaluate the effect of non-genetic factors such as the period of calving, season of calving, and parity on economically important productive and reproductive traits in crossbred cows (Holstein Friesian × Sahiwal) maintained at livestock experiment station Qadirabad Sahiwal, Pakistan. The study ranged from 1995 to 2014 (20 years). The duration of 20 years was divided into 4 periods (P1, P2, P3, and P4) with each period consisting of five years. Each year was further divided into three seasons winter (November-February), summer (March-June), and spring (July-October) based on geo-climatic conditions prevailing in the region. The parameters used as indicators of reproductive performance in this study were age at first calving (AFC), days open (DO), dry period (DP) and calving interval (CI). The overall least squares mean and standard errors for these reproductive parameters were 1235.23±45.81, 202.08±6.75, 178.4±6.85 and 482±5.97 days, respectively. While productive parameters were lactation milk yield 305 d(LMY), daily milk yield, and Lactation length (LL), and the least squares mean and standard errors of these were 2471.44±78.44 kg,8.07±0.27kg and306.22±4.84 days, respectively. Twenty years (20) data of 641 lactation records of crossbred cows representing the variance analyses indicated that significant (P≤0.05) effect of season of calving on age at first calving (AFC), days open (DO), lactation length (LL), and lactation milk yield (LMY). Least-squares means illustrated that the period of calving also significantly (P≤0.00) affects lactation milk yield (LMY) lactation length (LL) and dry period (DP). Similarly, a significant (P≤0.00) effect of parity on lactation milk yield (LMY), dry period (DP), days open (DO), and calving interval (CI) was noted. It is therefore concluded that the reproductive and productive performance of these crossbred cows is affected by some non-genetic factors and breeders must consider the season of calving, period of calving and parity in the management program because they greatly affect the farm productivity and profitability and they must select animals with higher breeding values to be the parent of the next generation.


INTRODUCTION
In dairy cows, productive and reproductive traits that determine the profitability of dairy production are age at first calving, days open, calving interval, dry period, lactation length, and milk yield, etc. (Lobago et al. 2007).These economically significant traits are influenced by genetics and non-genetic factors (Abou-Bakr,2009).Calving season, parity, management, and the production sector are the main nongenetic factors that might impact these traits.(Epaphras et al.2004).
Age at first calving is one of the important reproductive traits that contributes to economic return.Reduction in AFC will minimize the raising costs, shorten the generation interval, and subsequently maximize the number of lactations per head.(Singh et al.1986).Another important reproductive trait is days open (DO), and it is interval between date of calving and date of conception (Arbel et al. 2001).Days open directly affect calving interval (CI), which plays an important role in the profitability of dairy farms (Amene et al.2011 andNoakes et al.2001).Similarly, the dry period (DP) is necessary for compensation of the depleted nutrients during lactation and typically 40 to 60 days of dry period is believed to be required to maximize milk yield in the subsequent lactation (Santschi et al. 2011 andSosa et al.2012).Meanwhile, Milk yield, lactation length and calving interval are also among the main productive traits that affect the economic profitability of dairy farms and several reports have indicated that poor reproductive performance such as prolonged calving intervals can result in reduced milk yield and increased culling rates (Potdar et al.2020).The short service period reduces the generation interval and increases the genetic gain per unit of time (Santschi et al. 2011).Service period, lactation length, dry period, milk production and calving interval have a great economic importance as breeding efficiency (Hadad et al.2020).Hence, to improve these productive and reproductive traits for economical dairy farming, the study of non-genetic factors such as year of calving, season of calving and parity is very important (Wondifraw et al. 2013).
Collectively, number of studies involving comparisons of productive and reproductive performances have been conducted (Das et al. 2009;Khan et al. 2005: Hossain et al. 2002) but there are very few studies on factors affecting the economic dairy traits (Rehman et al. 2008;Fadlemoula et al. 2007 andSattar et al. 2005).In Pakistan, very scanty work has been reported so far on factors influencing the productive and reproductive performances in crossbred dairy cows.Therefore, this study was an attempt to know the effect of different non genetic factors such as season of birth, year of birth and lactations on economically important dairy traits such as age at first calving (AFC), days open (DO), calving interval (CI), lactation length (LL), Dry period (DP) and lactation milk yield (LMY) in crossbred dairy cows maintained at livestock experiment station Qadirabad Sahiwal, Pakistan.

MATERIALS AND METHODS
The study area: This study was conducted at Livestock experiment station Qadirabad Sahiwal, Pakistan.It is situated approximately between 30.0442° to 30.6682° N and 72.3441° to 73.1114° E. (Jahangir et al. 2016).The conditions are semiarid where May, June, and July are the hottest months, with average temperatures ranging from 38 °C to 48 °C with occasional extreme temperatures of 55 °C.The coldest months are December and January, with an average lowest temperature ranging from 5 °C to 22 °C.The average annual rainfall ranging from 150 to 300 mm and average annual temperature is 27.9 °C with minimum 10.3 °C and maximum 45.5°C, respectively (Waseem et al. 2022 andZareen et al. 2012).
Data management: Data screening was made to prevent human error in data entry on individual animal cards or in computer writing.In order to analyze LMY, DMY, and LL, the minimum cutoff point for LL in this study was 100 days, which was considered incomplete lactation.Due to a paucity of information, lactation records from parities eight and above were combined into eighth parity.The crossbred cows having abnormal calving, i.e., abortions and stillbirths were not included in the analysis.

Data analysis:
The General Linear Model (GLM) procedure of Statistical Analysis System (SAS 2004) version 9.0 was employed to determine and compare the fixed effects of different calving periods, calving seasons and parity for AFC, LMY, DMY, DO, CI, GP and LL traits.The normality of data was checked.The years of calving ranged from 1995 to 2014 were grouped into 4 periods.Thus, each period consisted of 5 years.For season of calving, months of the years were classified into 3 seasons based on rainfall distribution as dry season from October to February, short rain season from March to May, and main rain season from June to September.The presences of any significant differences among fixed effects (non-genetic factors) were checked using least square mean separation of SAS procedure.The productive and reproductive traits were analyzed by the following model; Yijkln = μ + Yi + Sj + Pk + eijkl Where; Yijkn =nth record of, ith period, jth season, and kth parity μ = overall mean Yi = effect of ith period of Calving Sj = effect of jth Season of Calving.Pk = effect of kth Parity of Dam (1,2,3,4,5,6,7,8) eijkl = random error associated with each observation

RESULTS AND DISCUSSION
The overall mean of all traits for crossbred dairy cows in different seasons of birth, years of birth and lactations are shown in the table1 to 3 and figures 1 to 2.

The effect of period of calving on days open (DO):
In the present study, a nonsignificant (P>0.28)effect of period of calving on days open were observed.Thombre (1996) and Chauhary et al. (1989) both reported similar outcomes.On the other hand, days open were found to be influenced by period of calving (P<0.01)(Basu and Ghai 1980).The days open were shorter in the fourth and sixth periods, and longer in the second and third periods.This might be due to husbandry, health care and nutritional variations between the farms.(Chauhary et al.1989 andMudgal et al. 1986).An environment that includes management, feeding, and breeding appears to be a major factor in the variation in mean DO values.

The effect of season of calving on days open (DO):
The effect of period of calving on dry period (DP): Dry periods were shown to be statistically significant (P<0.00) in this analysis, with the longest (215.94±11.44)occurring in period P-1(1995 to 1999) and the shortest (128.56±.9.32) in period P-5 (2009 to 2014).In an additional investigation, the calving period had a substantial impact on the dry period of HF × Deoni crossbred cows (P<0.01).While there was no statistically significant difference between the other periods, the dry period was longer during the study's second and third phases.The findings of Komatwar et al. (2010) and Mudgal et al. (1986) were comparable.The effect of the calving period on the dry period, however, was found to be non-significant by Auradkar (1999).

The effect of season of calving on dry period (DP):
A recent study found that the dry period was influenced by the season of calving (P<0.00).It was longest in summercalved cows (218.52±) and shortest in winter-calved cows (177.01±).Similarly, the dry period of HF × Deoni crossbred cows was also significantly (P<0.01)affected by the season of calving; the cows that calved in winter and post-monsoon season had the shortest dry period.Similar findings were reported in different crossbred cows by Auradkar (1999) and Chenyambuga and Mseleko (2008), while Mudgal et al. (1986) and Komatwar et al. (2010) reported that the season had no effect on the dry period.
The effect of parity on dry period (DP): According to the current data, parity had a substantial (P<0.01)impact on the dry period.The first lactation had the largest mean dry period (213.8±14.82),whereas the third lactation had the shortest (141.11±15.2).The current result was consistent with results by Komatwar et al. (2010) and Mudgal et al. (1986).On the other hand, Patil (1997) found that parity had no discernible impact on the dry time in various crossbred cows.

The effect of period of calving on calving interval (CI):
In crossbred cows, the calving period had significant (P<0.01)effect on the calving interval.Cows calving during period 3 had the largest calving interval (513.778±), while cows calving during period 2 had the smallest (472.89±).Dahiya et al. reported similar outcomes (2003).However, Auradkar (1999) and Chavan (2001) found no evidence of a significant relationship between the calving interval and the period of calving in various crossbred cows.

The effect of season of calving on calving interval (CI):
Crossbred cows' calving interval was not significantly affected by the calving seasons (P>0.12).Deshmukh (1996) reported a similar finding.On the other hand, Auradkar (1999) and Dahiya et al. (2003) noted a noteworthy impact of the calving season on the calving interval in various crossbred cows.

The effect of parity on calving interval (CI):
The calving interval in crossbred cows was significantly (P<0.01)affected by parity.The longest calving interval (523.21±20.96)was observed in the first lactation, while the shortest (441.75±18.3)was noted in the 2nd lactation.Similar finding was reported by Nehra et al. (1987).However, Latpate (1995) and Deshmukh (1996) reported non-significant effect of parity on calving interval in different crossbred cows.A calving interval of 365 days is usually considered ideal (Khan et al.1992).Therefore, the calving intervals, as seen in this study were somewhat longer which needs an improvement in overall management of the dairy cows.Sewalem et al. (2008) indicated that poor reproductive performance, manifested as prolonged calving intervals, which can result in reduced milk yield and increased culling rates and replacement cost.

The effect of period of calving on lactation length (LL):
Our results are in agreement with Bhutkar et al.

The effect of season of calving on lactation length (LL):
In our findings, the effect of seasons of calving on the lactation length in crossbred cows was significant (P<0.00).Lactation length was shortest in summer calvers (287.46±9.35)and longest in cows calved in winter (328.02±11.42).Our results are coincided with Usman et al. (2012) who reported that season has effect on lactation length (366.5±76.71) in Holstein cows and in this study lactation length is greater than present study it may be due to breed difference.
The effect of parity on lactation length (LL): Lactation length was not (P>0.55)affected by parity in our study.However, Mohamed et al. (2017) reported that parity has effect (P<0.05) on lactation length.Cows in first, second and third parity had higher total milk yield, daily milk yield, and corrected milk yield (305 milk yield) than subsequent lactations.The difference from others findings might be due to difference in environmental condition, number of observations taken for the study and level of management practices.

The effect of period of calving on lactation milk yield kg, (LMY-305d):
The lactation milk yield 305 d in crossbred cows was significantly (P<0.00)affected by period of calving.The largest milk yield (3483.17±237.22) was observed in the cows calved during period 5(2009 to 2014), while the low milk yield (2165.97±137) was found in period 2 (2000 to 2004).

The effect of season of calving on lactation milk yield kg, (LMY-305d):
As indicated in fig.2,the effect of season of calving on 305 d milk yield was significant (P<0.00).The largest milk yield (2606.26±67.57)was observed in the cows calved during winter, while the low milk yield (2223.22±64.4)was found in summer.These results are close to similar in Crossbred cows reported by Amasaib et al. (2010) The effect of parity on lactation milk yield kg, (LMY-305d): The calving interval of crossbred cows was significantly (P<0.04)affected by parity.The largest milk yield (2614.17±18.49) in 305 d was observed in the 5th lactation, while the smallest was noted in the first lactation (2225.76±16.2).Bhutkar et al. (2014) also concluded that party have effect on lactation milk yield.

The effect of period of calving, season of birth and parity on daily milk yield (DMY):
The daily milk yield in crossbred cows was insignificantly (P>0.40)affected by period of calving, season of birth and parity These findings are inconsistent with finding of Amasaib et al.
(2010) who reported that parity have effect on daily milk yield.The difference from others findings might be due to difference in environmental condition, number of observations taken for the study and level of management practices.

The effect of period of calving, season of birth and parity on Gestion period (GP):
The Gestion period in crossbred cows was insignificantly (P>0.11)affected by period of calving, season of birth and parity.Similar finding was reported by Chakrabortty et al. (2018) and Amasaib et al. (2010) Effect of Season of birth on Age at First (AFC days): In this study, significant effect of season of birth (as indicated in fig. 1) was found on age at first calving in crossbred cows (P<0.05).Age at first calving in rainy season (July to October), was lowest (1145.19±22.1)while in Summer (March-June) AFC was longest (1294.93±41.03).Similarly, significant effect of season of birth was reported by Hadia et al. (2011) in Girolando cattle and Kumar (2007) Dahiya et al. (2003) also reported a non-significant effect in Sahiwal cattle and Crossbred cattle respectively.This difference might be due breed which was used for cross breeding.

Fig. 1 :
Fig.1: Effect of season of calving on AFC commencing from 1995 to 2014 (20years).SEM=standard error of mean AFC=age at first calving, Summer = March to June; Rainy=July to October; Winter=November to February; different superscript (large letter) is significant at (P ≤ 0.05).The error bars reflect the SEM for AFC associated with season of calving in cross bred cows (HFxSahiwal).
In this study, significant(P<0.02)effect of calving season on days open was observed.The cows who calved in the rainy had the shorter days open (193.5±10.41),while longer days open (225.89±08) was observed in winter season.(Table 1.) Pyne et al. (1988) and Chauhary et al. (1989) reported similar results.Nonetheless, Thombre (1996) found that the calving season had no discernible impact on the number of open days.The variance in days open owing to calving season could be explained by variations in seasonal feeding schedules and climate.
examined significant influence (P<0.01) of season of birth on age at first calving in Sahiwal cattle, respectively.Contrary to present result, non-significant effect of season of calving was reported by Nikhil et al. (2014) in Gir cows, Pareek et al. (2016) in Kankrej cows and Ravi et al. (2018) in Gangatiri cows.Sivamani et al. (2013) and

Table 2 . Effect of period of birth on productive and reproductive traits of cross bred cows.
SEM=Standard error of mean.Means within the same row carrying different superscripts (large letters) are significantly different (P≤0.05).DO=Days open in days; CI=calving interval in days; LL=lactation length in days; GP=Gestion period in days; DMY=Daily milk yield and LMY=lactation milk yield 305 d in kg.Productive traits=LMY, DMY, LL; Reproductive traits=AFC, DO, DP,CI,GP.

Table 3 . Effect of parity on productive and reproductive traits of cross bred cows.
Effect of parity(lactation#) on productive and reproductive traits commencing from 1995 to 2014 (20years).SEM=standard error of mean.Means within the same row carrying different superscripts (large letters) are significantly different (P≤0.05).DO=Days open in days; CI=calving interval in days; LL=lactation length in days; GP=Gestion period in days; DMY=Daily milk yield and LMY=lactation milk yield 305 d in kg; Productive traits=LMY, DMY,LL;Reproductive traits=AFC,DO,DP,CI,GP.