A total 1481 first lactation records of local born Friesian heifers were collected from Sakha Farm, Animal Production Research Institue, Ministry of Agriculture, during the period from 1980 to 1993. A linear mixed model was used to study the fixed effects of month and year of calving, age at first calving as a covariate and the random effect of sire on productive traits (i.e., 90 day milk yield (90dMY), 305 day milk yield (305dMY), total milk yield (TMY), lactation period (LP) and dry period (DP)). The effects of the same factors on reproductive traits (i.e., days open (DO) and calving interval (CI)) were also studied. Least squares means of 90 dMY, 305 dMY, TMY, LP, DP, DO and CI were 959 kg, 3252 kg, 3709 kg, 367 d, 65 d, 145d and 426d, respectively. A least squares analysis of variance showed significant effect of month of calving on 90 dMY, 305 dMY, TMY and LP (p<0.05 or p<0.01). Year of calving had a significant effect on all traits studied (p<0.05 or p<0.01). Including age at first calving (AFC) as a polynomial regression of the second degree in the model yielded significant (p<0.05 or p<0.01) partial linear regression coefficients of 90 dMY, 305dMY, TMY and DP on AFC while the quadratic term was significantly only for 305dMY. Sire of the heifers had a significant effect on all productive traits. Heritability estimates for 90dMY, 305dMY, TMY, LP, DP, DO and CI were 0.30 ± 0.08, 0.30 ± 0.08, 0.15 ± 0.06, 0.10±0.06, 0.09±0.06, 0.05±0.06, 0.05±0.06, respectively. In addition, genetic and phenotypic correlations between different traits studied are calculated and tabulated. Negative genetic correlations between each of DP, DO and CI and 90dMY, 305dMY and TMY concluded that selection against dry period and days open will increase milk yield. Therefore, a reduction of DP and DO are the desirable goal of dairymen.
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Milk yield and fertility traits are the principal factors affecting profitability of a dairy herd. Early postpartum breeding in dairy animals, high fertility, short dry period and early maturity are resulted in more calves and high milk yield per unit of time throughout the herdlife (Britt, 1975). The genetic importance of fertility in dairy cattle should be evaluated for its direct effect on cows reproductive performance and its association with milk yield. Olds et al. (1979), Janson (1980), Khattab et al. (1987), Kafidi et al. (1992), Bagnato and Oltenacu (1993) and El-Nady (1996) concluded that fertility traits have low heritabilities, generally between 0.01 and 0.10, indicating that little genetic improvement for reproductive performance can be expected.
Negative influence of level of milk production on fertility has been observed by numbers authors Everett et al. (1966), Olds et al. (1979), Janson (1980), Afifi et al. (1992), Kafidi et al. (1992) and Soliman and Hamed (1994). In addition, Hansen et al. (1983) found that selection for fertility is possible but it will generally be associated with a decline in production and concluded it was not economically feasible. On the other hand, Seykora and McDaniel (1983) concluded that selection for the improvement of reproductive performance could be economically justified. The objectives of this work are estimate nongenetic factors affecting productive and reproductive traits and estimated the phenotypic and genetic parameters for the same traits in a local born Friesian cattle in Egypt.
MATERIALS AND METHODS
A total of 1481 first lactation records of local born Friesian cattle were used for the present study. Animals are a part of the herd of Sakha Farm Animal Production Research Institute, Ministry of Agriculture. Records were produced during the period 1980 to 1993, inclusive. Abnormal records affected by diseases or by disordes such as abortion were excluded. Productive traits studied are 90 day milk yield (90dMY), 305 day milk yield (305dMY), total milk yield (TMY), lactation period (LP) and dry period (DP). Reproductive traits are days open (DO) and calving interval (CI). The number of sires and the average of daughters per sire were 128 and 10.94, respectively. Genetic analysis included the sires which have at least 5 daughters. Artificial insemination (Al) was used at random.
Cows of that herd were kept under a regular system of feeding and management adopted by the Research Center, Ministry of Agriculture. Animals were grazing on Egyptian clover (Trifolium alexandrinum), berseern during December to May, during the rest of the year they were given pelleted concentrates and rice straw. Heifers were attempted for service for the first time when they reached 18 mo or 350 kg. Rectal palpation for pregnancy diagnosis was performed 60 days after the last service. Cows were machine milked. Records incuded number of days open, which was computed as the interval between parturition and the date of successful mating or by subtracting the mean of gestation period estimated from the present date as 285 days from the normal calving if the date of successful mating was not known. Length of dry period was computed by subtracting the date of last milking from the next calving of date. Records with missing drying off date were rejected. The period between two consecutive calving is known as calving interval, which includes the days open and the gestation length. For the least squares analysis of variance the following general linear model was used:
Y = Xb + Zs + Wb + e
where Y was a vector of observations for each of the traits, X was a known fixed design matrix, b was an unknown vector of fixed effects repesenting the mean, month and year of calving, Z was a known design matrix, s was a vector of covariate variable (age at first calving), b was a vector of partial regression coefficients of Y on W and e was an unobserved random vector of errors with mean zero and variance 1σe2.
Estimates of sire and remainder components of variance and covariance were computed according to Harvey (1987). Estimates of heritability (h2) was calculated as four times the ratio of σs2 (sire variance compontents) to the sum of σs2 + σe2 (remainder variance components). Standard errors of h2 was calculated using an approximate formula described by Swiger et al. (1964). Genetic and phenotypic correlations were estimated as described by Harvey (1987).
RESULTS AND DISCUSSION
Least squares means: Least squares means of different traits studied are presented in Table 1. Mean; reported here for 90 dMY (959 kg), 305dMY (3252 kg) and TMY (3709 kg) are higher than those reported for Friesian cattle raised in Egypt by (Khattab and Sultan, 1991; Afifi et al., 1992; Khalil et al., 1994; Abdel Glil, 1996). Khalil et al. (1994) found that mean of 90dMY, 305dMY, TMY (600 kg, 2384 kg and 2577 kg), respectively. While, the present means of 90dMY and 305dMY are lower than those reported by Hussen (1996) using a commercial herd of Holstein Friesian cattle in Egypt, being 1748 kg and 4938 kg, respectively. Also, Atay et al. (1995) and Kaya (1996) working on Holstein Friesian cattle in Turkey found that 305 dMY were 5480 kg and 5444 kg. In addition, Onenec (1997) working on Holstein Friesian cattle in Turkey found that 305dMY and TMY are 4789 kg and 4865 kg, respectively. For subtropical Arabian countries, Mansour (1992) with Holstein Friesian in the Kingdom of Saudi Arabia, reported higher means than those obtained here. Low milk yield of Friesian cows during the earlier period after importation may reflect the source of importation and may be due to the heat stress to which lactating cows were exposed since they need some time to adapt in subtropical and semi-arid areas.
In terms of lactation intervals, means of LP reported here (367 d) for Friesian falls with the range from 315 to 363 d for Egyptian reports (Ragab et al., 1973; Khattab and Sultan, 1991; Afifi et al., 1992; Khalil et al., 1994, El-Nady, 1996; Abdel Glil, 1996 and El-Awady, 1998). In Turkey, Atay et al. (1995) and Onenec (1997) reported that mean of LP are 339 and 287 d, respectively. Mean of DP (85 d) is shorter than those of Friesian cattle reported of the Egyptian studies (Afifi et al., 1992; Khalil et al., 1994; El-Nady, 1996).
Gill and Allaire (1976) found that maximum profit per day of herd life is expected for cows with 42 days dry. Khalil et al. (1994) found high coefficient of variability for DP (72.45%) they concluded that DP is mostly governed by environment and management of the herd which could bring down the DP in Friesian cattle in Egypt. The present means of DO and CI are 145 and 427 d (Table 1). The present means are similar to those obtained by El-Sedafy (1989) using another herd of Friesian cattle in Egypt. Khattab and Ashmawy (1988) suggested that days open length of 60-90 days was optimum length for attaining maximum production for Friesian cattle in Egypt.
The differences between our results and those of other workers could be due to differences in climatic and management conditions and/or genetic differences in herds.
Fixed effects: Morith of calving had a significant effect on productive traits (90 dMY, 305 dMY, TMY and LP, Table 2, p<0.05 or p<0.01), while, DP, DO and CI are not affected by month of calving. The present results are agree with those of Ragab et al. (1973), Ashmawy et al. (1986), Rege (1991), Abdel-Bary et al. (1992), Kafidi et al. (1992), Khattab (1992), Khalil et al. (1994), Gad (1995), El-Nady (1996), Malau-Aduli et al. (1996) and El-Awady (1998).
The highest frequency of calving were observed from December through May. It is noticed that the dairymen in Egypt concentrated their calving in winter months have the highest performance of milk trait, while those calving in summer months showed the lowest. The high 90dMY, 305dMY and TMY and longer LP in winter calvers could be attributed to the favourable climatic conditions for abundant growth and availability of good quality Egyptian clover (Berseem) during increasing stage of lactation. Also, heifers calving on winter and spring months had shortest DP, DO and CI, than heifers calving during summer and autumn. Poor results in breeding efficiency in summer are attributed to the high indicate of silent heat making detection of oestrus more difficult and to deficiency of Vit. A. Also, Rege (1991) working on Friesian cattle in Kenya, concluded that seasonal of variation in animal performance in the tropics is expected to be primarily a manifestation of variation in feed quality and quantity. El-Fouly et al. (1976) reported that preparing the animals to have the full chance for conception during the season of full ovarian activity (October-May) reduce DO considerably. While, Khalil et al. (1992) on Egyptian buffaloes found that summer calvers had the highest 90dMY and 305dMY. On the other hand, Eltawil et al. (1976) observed a consistent trend in season of calving effect on milk yield although not attaining statistical significance in most cases.
Year of calving had a significant effect on all traits studied (Table 2). The present results are agree with the findings on Friesian cattle raised in Egypt as reported by Ragab et al. (1973), Ashmawy and Mokter (1984), Afifi et al. (1992), Khattab (1992), Gad (1995), El-Nady (1996) and El-Awady (1998). The same findings are also reported on Friesian cattle raised in other countries by Sharma et al. (1987), Rege (1991), Kafidi et al. (1992), Atay et al. (1995), Lefton and Patina (1995), Kaya (1996), Malau-Aduli et al. (1996) and Kaygisiz (1997).
|Table 1:||Least squares means (LSM) and standard errors (S.E.) for factors affecting productive and reproductive traits in a local born Friesian cattle|
|Table 2:||F-ratios for factors affecting productive and reproductive traits|
|Table 3:||Estimates of heritability, genetic correlations (below diagonal) phenotypic correlations (above diagonal) for productive and reproductive traits|
In addition, Metry et al. (1994) working on Egyptian buffaloes found that' year of calving had a significant effect on TMY, LP, DP, DO and Cl. Also, Soliman and Hamed (1994) found significant effect of year of calving on productive and reproductive traits on Braunvieh cows, they concluded that the least squares means of year of calving shows that was an upward trend in all traits studied, the upward trend is probably due in part to genetic improvement and partly due to improved feeding and management.
The present results show that change in production and reproductive traits studied from year to year can be attributed to change in herd size, age of animals, improved management practiced introduced from year to another and phenotypic trend. Also, the present results Table 1, show that 90dMY, 305dMY and TMY increased from about 770 kg, 2500 kg and 2800 kg in the early eighty to nearly 870 kg, 2800 kg and 3300 kg in the ninety, while, LP, DP, DO and CI in most cases decreases, this could be due to positive phenotypic trend in this herd. Abdel Glil (1996) working in the same herd, concluded that phenotypic trends for 305dMY, TMY and LP were 30 kg, 36 kg and -2.30 d, respectively. In recent years dairy cattle breeders in Egypt succeeded to improve the reproductive performance of their cows by reducing the CI through fixing lactation period and decreasing DP.
Estimates of partial linear regression coefficients of 90dMY, 305dMY, TMY and DP were significant, being 2.26 ± 0.50 kg/mo, 4.33 ± 1.54 kg Imo, 5.17 ± 2.50 kg/mo and 0.22 ± 0.02 d/mo, respectively (Tables 1 and 2), while, the quadratic terms were not significant on all traits, except for 305dMY (-0.145±0.06 kg/mo). The curvilinear relationship of 305dMY on AFC are reported by Sallam et al. (1990), Khattab and Sultan (1991) and Abdel Glil (1996) using another sets of Friesian cattle in Egypt. Also, Ashmawy and Mokter (1984) and Afifi et al. (1992) working on British Friesian and Holstein Friesian cattle, respectively. While, Ashmawy et al. (1986) found that the linear regression coefficients of 305 day milk on AFC was positive and significant (18.82 kg/mo). The youngest first calves (26 mo) produced the lowest yield while, the oldest ones (42 mo) produced the highest yield .It is not justified to bring heifers into calving at an unduly old age although their first milk yield will increase because this results in decreasing the longevity and increasing the rearing the heifers. Also, Soliman and Hamed (1994) found that cows freshening at 40 month or more had the highest yield traits, while, the lowest productions was recorded for cows calved at 24 month of age.
The prediction curve based on the second degree polynomial regression of 305dMY with increasing in AFC. The present results indicate that increase in 305dMY with increase of AFC up to 40 mo and then decline. Therefore, a reduction in AFC is desirable for dairy breeders to prolong the length of herdlife and to economize the cost of heifers. Also, Ali et al. (1999) working on Nili Ravi Buffaloes, found that reduction in AFC will help to improve lifetime milk yield, longevity and reproductive ability as a correlated response. On the other hand, Schaefer and Henderson (1972), Basu and Ghai (1980), Sharma et al. (1987) and Abdel Glil (1996) found no significant effect of AFC on DO and Cl.
F-ratios presented in Table 2 indicate that year of calving and AFC are considered the major factors affecting 90dMY, 305dMY, TMY, LP and DP. Afifi et al. (1992) came to the same conclusion using another data set from commercial Friesian herds. This leads to conclude that adjusting of lactation records for year of calving and AFC are very necessary for sire, evaluation.
Random effect: Sire of the heifers had a significant effect on productive traits (p<0.05 or p<0.01). These results are in agreement with those reported in the literature (Berger et al., 1981; Hansen et al., 1983; Sallam et al., 1990; Khattab and Sultan, 1991; Rege, 1991; Afifi et al., 1992; Kafidi et al., 1992; Metry et al, 1994; Gad, 1995; El-Nady, 1996; Abdel Glil, 1996; El-Awady, 1998). In practice, the present and reviewed studies concluded that the possibility of genetic improvement of milk through selection.
Genetic and phenotypic parameters Heritability estimates: Estimates of heritability (h2) for different traits studied are presented in Table 3. Estimates of h2 for. 90dMY, 305dMY and TMY are 0.30 ±0.08, 0.30 ± 0.08 and 0.15 ± 0.06, respectively. Similary, Afifi et al. (1992) reported a corresponding estimate of 0.30 and 0.30 for 305dMY and TMY, respectively using another set of Friesian cattle in Egypt. Also, Ragab et al. (1973), Swalve and van Vleck (1987) and El-Nady (1996) reported that h2 for 305dMY are 0.33, 0.33 and 0.36, respectively. In Turkey, Kaya (1996) working on four herds of Holstein cattle, found that h2 for initial milk yield, 100 day milk yield and 305 day milk yield were 0.19, 0.24 and 0.19 for Tahirova herd, 0.32, 0.35 and 0.31 for Dalaman herd, 0.25, 0.23 and 0.26 for Turkgeldi herd and 0.11, 0.13 and 0.17 for Sarmisakli herd. According to moderate h2 for milk traits it can be concluded that the genetic improvement in milk production can be achived through selection programme.
The estimate of h2 for LP was 0.10 ±0.06. The present estimate in agreement with those of Ragab et al. (1973), Afifi et al. (1992), El-Nady (1996) which ranged from 0.05 to 0.15. The present results indicate that the major part of variation in this character is due to nongenetic factors and great improvement in LP could be possible by imroving feeding and management systems. For DP, h2 estimates was 0.09±0.06, Kornel and Patro (1988) with Surti buffaloes, found that DP had negative h2 estimate in four lactations meaning that the estimation is zero improving in management would be needed to decrease this trait. Basu and Gliai (1980) found that differences in DP between sire were not significant. El-Nady (1996) found that h2 for DP was 0.02. Also, Metry et al., (1994) found that h2 for DP was zero.
Heritability estimated for DO and CI are 0.05 ± 0.06 (Table 3). The low h2 estimates for reproductive traits indicate that a major part of variation in these characters were environmental and selection would be not effective in bringing about genetic improvement. Better management can therefore play an important role in improving such trait. Therefore, improving the managerial technique should lead to a considerable in the length of reproductive traits. The present results are within the range obtained by Smith and Legates (1962), Everett et al. (1966) (0.07), Schaefer and Henderson (1972) (0.02-9.03), Khattab et al. (1987) (0.06), Afifi et al. (1992) (0.08), Bagnato and Oltenacu (1993) (0.03), Metry et al. (1994) (0.00) and El-Nady (1996) (0.01). Schaefer and Henderson (1972) reported that effect of days open on milk yield was almost all environmental. Khattab and Ashmawy (1988) concluded that selection for improved fertility defined as DO had little to offer to breeders. Low h2 estimates of DO which is essentially zero, adjusted if lactation records for days open would not involve genetic influence on yield and or on sire and cow evaluation.
Correlations: Genetic correlations (r9) and phenotypic correlations (rp) between different traits studied are given in Table 3. Genetic correlations between 90dMY and each of 305dMY, TMY and LP also, between 305dMY and each of TMY and LP are positive and significant. The present results indicate that the initial milk yield could be used as indicators to early selection progress. Also, the genes associated with long lactation period are correlated with genes favourable for milk yield and selection against short LP is also expected against low production. The present results are in agreement with similar work on Friesian cows in Egypt (Ragab et al., 1973; Khattab et al., 1987; Hussen, 1996; Abdel Glil, 1996). Negative genetic correlations between productive traits (i.e., 90dMY, 305dMY and LP) and DP and all reproductive traits (DO and CI), except LP with CI, indicate that selection for short DP, DO and CI will lead to increase milk production. The present results are agreement with Schaefer and Henderson (1972), Afifi et al. (1992), Khattab et al. (1987) and Rege et al. (1991), while, Kragelund et al. (1979) found a high genetic correlations (0.62 to 0.72) between days open and milk yield in three analysis (based on a minimum of 2, 50 and 50 cows per sire) suggested a close relationship between breeding value of milk yield and days open. Genetic correlations between DP and each of DO and CI are positive and being 0.44 and 0.14, respectively.
Basu and Gahi (1980) reported that DP was positively correlated with CI and DO. Kragelund et al. (1979) and Afifi et al. (1992) reported positive rg between DO and Cl. The present results indicate that DO serves the same purpose as CI for evaluation of the reproductive performance of dairy breeders. Most estimates of rp are similar to the corresponding estimates of rg in the same direction, High positive rp between 90dMY, 305dMY, TMY and LP indicate that 90dMY can be used for evaluating the milk producing ability in cows. Negative rp between milk traits and DP and DO indicate that cows with shorter DP and DO with shorter LP will produce more milk during the first lactations. Finally, it is concluded from the present study that short dry period and days open will increase milk production, also, low h2 estimates for reproductive traits indicate that little improvement for reproductive traits for Friesian cattle in Egypt can be expected.
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