Effects of non-lactating period length on the subsequent calving ease and reproductive performance of Holstein, Brown Swiss and the crosses

Effects of non-lactating period length on the subsequent calving ease and reproductive performance of Holstein, Brown Swiss and the crosses

Animal Reproduction Science 158 (2015) 60–67 Contents lists available at ScienceDirect Animal Reproduction Science journal homepage: www.elsevier.co...

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Animal Reproduction Science 158 (2015) 60–67

Contents lists available at ScienceDirect

Animal Reproduction Science journal homepage: www.elsevier.com/locate/anireprosci

Effects of non-lactating period length on the subsequent calving ease and reproductive performance of Holstein, Brown Swiss and the crosses Mahmoud S. El-Tarabany ∗ Department of Animal Wealth Development, Faculty of Veterinary Medicine, Zagazig University, Egypt

a r t i c l e

i n f o

Article history: Received 4 February 2015 Received in revised form 22 April 2015 Accepted 24 April 2015 Available online 4 May 2015 Keywords: Holstein Brown Swiss Fertility Production Non-lactating period

a b s t r a c t The aim of this study was to evaluate the effects of the non-lactating period (NLP) length on the subsequent calving ease and reproductive performance of the purebred Holstein (HO), Brown Swiss (BS) and F1 crosses (BF) of these breeds. The NLP length was classified into four categories: D1 : <45 d; D2 : 45–60 d; D3 : 60–75 d; and D4 : >75 d. The lesser incidence of calving difficulty in the purebred HO and BF crossbred cows was recorded at D3 , with no significant differences with D2 [11.6% and 9.5%; Crude Odds Ratio (COR) = 1.10 and 0.84, respectively]. However, the minimum incidence of calving difficulty in the purebred BS cows was at the same NLP length with significant differences with D2 (3.8%; COR = 0.31). All reproductive indices of the purebred HO cows were less as the NLP length increased. However, lesser estimates of calving interval and days non-pregnant in purebred BS and BF crossbred cows were recorded at longer (D3 ) NLP (350 and 328 d; 112 and 133 d, respectively). Purebred HO cows had decreased milk production at extremely short (D1 ) and long (D4 ) NLP. Purebred BS cows, however, were more persistent in milk production and had more consistent body condition scores (BCS). In conclusion, shortening the NLP of the purebred HO cows in addition to making minimum changes in diet composition could be an appropriate solution for improving reproduction. Purebred BS and BF crossbred cows were more persistent in milk production and tolerated the diet changes during the NLP. © 2015 Elsevier B.V. All rights reserved.

1. Introduction Reproductive efficiency in high producing dairy cows has been reduced in recent decades (Royal et al., 2000; Butler, 2003; Evans et al., 2006). Intensive genetic selection for improved milk production has led to greater milk yields per cow but has also been related with a worldwide

∗ Correspondence to: Department of Animal Wealth Development, Faculty of Veterinary Medicine, Zagazig University, El-Zeraa str. 114, 44511 Zagazig, Egypt. Tel.: +20 1223668785; fax: +20 552283683. E-mail addresses: [email protected], [email protected] http://dx.doi.org/10.1016/j.anireprosci.2015.04.008 0378-4320/© 2015 Elsevier B.V. All rights reserved.

decrease in dairy cow fertility. There is a negative correlation between the genetic trait for milk yield and reproductive performance (Van Arendonk et al., 1989; Pryce et al., 1997; Pryce and Veerkamp, 2001). The decrease in fertility is probably due to a combination of physiological and management factors that have an additive effect on reproductive efficiency (Lucy, 2001). The non-lactating period (NLP) for pregnant dairy cows is recommended between sequential lactations based on the nutritional requirements of the late pregnant cow and to permit appropriate involution of the mammary gland epithelium to maximize milk yield during the subsequent lactation. Furthermore, papillae of the rumen and the small intestine are regenerated during the NLP and the gut microbial populations of the

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cow are changed so as to contribute in providing for an increased nutrient requirement of the mammary gland during lactogenesis (Annen et al., 2004; Church et al., 2008). The NLP also allows for the application of an extended intra-mammary antibiotic therapy to minimize the prevalence of existing infections and reduce the incidence of new infections (Eberhart, 1986). Many observational and experimental data have been generated to establish an optimal period for the NLP of cows (Gulay, 2005). The optimal duration of the NLP has been a subject of dispute with a period of 50–60 d given as the traditional recommended length (Bachman and Schairer, 2003; Church et al., 2008). However, because of management decisions related to gestation length and milk yield, it is common on many farms to have involuntary long or short NLP. In recent years, however, consideration has been given to shorter NLP, enabling additional income from milk yield at the end of lactation and an improved nutritional state to meet the physiological challenges of the transition period from non-lactation to lactation (Bachman and Schairer, 2003; Gulay et al., 2003). In addition, the shorter NLP may eliminate the need to separate non-lactating cows from the other cows and reduce the number of ration changes in the periparturient period and the associated stress. Conversely, greater production may also result in a demand for a longer NLP to maintain production, health and fertility in the subsequent lactation. Considerable research has been conducted regarding the effect of number of days of the NLP on subsequent lactation milk yield but far less research is available on the fertility aspects. Earlier studies demonstrated that short NLP resulted in decreased fertility as indicated by the additional 14 or more days before cows become pregnant (0–10 d NLP compared with 61–65 d NLP; Bachman and Schairer, 2003). Inconsistent with these findings is the reproductive performance of cows that have had three or greater numbers of lactations being improved at shortened NLP compared with the conventional NLP length (Watters et al., 2009). Length of the NLP might influence postpartum energy balance by potentially modifying reproductive performance. There is a relationship between energy balance and time of first postpartum ovulation with energy balance being an important factor for determining first postpartum ovulation and time of initiation of estrous cycles following calving. Furthermore, the first postpartum ovulation was reported to occur between 10 and 14 d after the energy balance nadir was reached (Canfield et al., 1990; Butler, 2003). Consistent with the relation between energy balance and days to first postpartum ovulation, reproductive performance of dairy cattle improved with an earlier initiation of estrous cycles after calving (Thatcher and Wilcox, 1973; Darwash et al., 1997; Staples et al., 1990); however, earlier reports indicated there was little or no change in reproductive performance with a shorter time to first ovulation after calving (Smith and Wallace, 1998; Royal et al., 2000). Dystocia was more prevalent in cows with NLP of >60 d compared with those with shorter NLP (Atashi et al., 2013). However, Enevoldsen and Sorensen (1992) reported that for cows with shorter NLP before becoming pregnant (0–88 d), the risk of calving difficulty was greater in cows with 10-wk NLP than in those with 7- or 4-wk NLP. Pezeshki

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et al. (2007), however, reported that decreasing the NLP from 56 to 35 d had no significant effect on dystocia. Shortening the NLP (to <40 d) minimizes milk yield (Coppock et al., 1974; Swanson, 1965). Similarly, recent retrospective studies indicated that reducing the NLP length resulted in a reduction in milk yield in the subsequent lactation (Bachman and Schairer, 2003; Watters et al., 2008; Mantovani et al., 2010; Atashi et al., 2013; Cermakova et al., 2014). When the NLP has been shortened, additional milk is produced in the ongoing lactation which may be advantageous if there is no yield depression in the subsequent lactation. Other studies indicated that the optimum NLP length may be shorter than previously considered and that a 30- to 40-d NLP is sufficient for maximizing milk yield in dairy cows (Bachman, 2002; Gulay et al., 2003; Pezeshki et al., 2007). However; lengthening the NLP (to >60 d) may increase costs and diminish the productive longevity of dairy cows (Hurley, 1989). Food intake and postpartum metabolic status of cows might be changed because of changes in diet and grouping of cows during the NLP (Collier et al., 2012). It has been suggested that cows with short or no NLP between two consecutive times of calving have improved dry matter intake, metabolic profiles, BCS, body weight and mean negative energy balance (Pezeshki et al., 2007; Watters et al., 2008). Furthermore, short NLP were associated with greater somatic cell scores during the subsequent lactation (Kuhn et al., 2006). However, one aspect that has received little attention, if any, in either past or recent research on NLP is whether breeds respond differently to variations in NLP length; virtually all research has been conducted using Holsteins. To the best of our knowledge, this is one of the few recent studies to investigate the effects of NLP length on the subsequent reproductive and production performance of crosses originating from two temperate breeds and managed under subtropical Egyptian conditions. Therefore, the objectives of the present study were to evaluate the effects of NLP length on the subsequent calving ease, reproductive and production performance of the purebred HO, BS and their F1 crosses under subtropical conditions. 2. Materials and methods This research was reviewed and approved by the Animal Care and Welfare Committee of Zagzaig University, Egypt (ANWD-206). 2.1. Animals and management This study was conducted at EXPANDED herd, Ismailia road, Cairo. To minimize health problems and overcome decreased fertility of Holstein (HO) cows, the breeders tended to cross with Brown Swiss (BS). Originally, the herd consisted of 1000 purebred HO and 112 BS cows. Crossing the two breeds resulted in 211 F1 crossbred cows (BF; 50% BS and 50% HO). All cows were housed in a dairy barn with sand-bedded free stalls, milked three times daily with yields recorded at each milking and pedometers being applied to all cows. The total mixed ration (TMR) was provided twice a day. The ration was mixed daily and modified according to the exact milk production and BCS of

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the cows. The TMR was formulated to meet the essential requirements of energy, protein, minerals and vitamins. The TMR was sampled monthly and analyzed by wet chemistry methods. The primary analysis of TMR include crude protein (16.91%), neutral detergent fiber (24.83%) and net energy for lactation (Mcal/kg = 1.76). Alfalfa hay was the primary forage. The diets during the NLP were formulated to meet or exceed the nutrient requirements established by NRC (2001). The reproductive data (insemination, reproductive problems, etc.) were recorded and tracked using a commercial on-farm computer software programs (AfiFarm version 4.1). For the farm area, the average minimum temperature in months of the cold season ranged from 9.5 to 11.8 ◦ C, and average maximum temperature was ranged from 19.6 to 21.7 ◦ C. The average minimum temperature for months of the warm season ranged from 21.9 to 23.8 ◦ C, and the average maximum temperature was ranged from 34.1 to 36.3 ◦ C.

records, each cow was assigned to an appropriate class for NLP. Before assigning cows to a date for initiation of the NLP, the cow’s milk production had to be ≥18 kg/d, days in milk <360 d and days non-pregnant <180 d. Such conditions have been considered to ensure the normal reproductive and production patterns at the time of initiation of the NLP. Furthermore, using these criteria allowed for minimizing possible effects of other variables than the NLP on the subsequent experimental outcomes. Calving ease is generally scored on a categorical scale designed to be practical yet minimizing for subjective interpretation. Scoring was conducted as normal: easy or minimum assistance but no calving difficulty; difficult: difficult with veterinary assistance (Kaya et al., 2015). A calf was considered stillborn if it was born dead, died during parturition or within 48 h of parturition.

2.2. Reproductive performance

The BCS was assessed 14 d after parturition. A visual scoring technique was used, giving a five-point scale (1 = emaciated to 5 = severely over-conditioned) with 0.25unit increments (Edmonson et al., 1989). Milk production of all cows included in the current study was monitored from the second to the fifth lactation. The 305 d actual milk yield (305-DMY) was recorded for all crossbred and purebred cows. Only data for complete lactations (305 d or more) were included. The actual 305-DMY is referred to the amount of milk produced during the first 305 d postpartum without any correction equation. The number of milk records for HO, BS and BF were 8220, 1470 and 2940, respectively.

According to the typical reproductive management practices for the farm, the breeding season extended from September to June. Cows were recorded to be in estrus if there was evidence of excessive activities through the pedometer records or visual inspection. Insemination occurred 14 h after detection of estrus and cows concomitantly received a dose of GnRH (10 ␮g, Buserelin; Receptal; Intervet). All purebred and crossbred cows were inseminated by four expert technicians with similar historical pregnancy rate efficiency records; using purebred HO semen. The HO semen was imported from progeny or genetically tested bulls. The main consideration for selection of bulls was calving ease index and the predicted transmitted ability for milk production, respectively. Ultrasonic examination was performed to determine the heifers or cows that were pregnant at 30 d post-insemination. A confirmatory pregnancy diagnosis was conducted at 75 d post-insemination. The reproductive performance including; date of calving, calving score, birth type (single, twin, stillbirth or abort), parity number, calving interval, days non-pregnant, and number of inseminations per pregnancy were recorded in the subsequent reproductive cycles over a period of 5 years between September 2008 and October 2013. The actual numbers of records for different genetic types are summarized in Table 1. The NLP was classified into the following categories; D1 : <45 d; D2 :45–60 d; D3 : 60–75 d; and D4 : >75 d. According to individual cow Table 1 Data description for different genetic types. Genetic type

Actual number of records

n HO BS BF

D1

D2

D3

AFC

GL

D4

6650 1420 2260 1995 975 28.6 ± 1.08 276.4 ± 2.6 880 126 264 352 138 29.7 ± 1.32 281.3 ± 2.4 1985 314 595 794 282 32.3 ± 1.16 276.7 ± 2.2

Non-lactating period length, D1 : <45 d; D2 : 45–60 d; D3 : 60–75 d; D4 : >75 d. AFC, age at first calving (mo); GL, gestation length (d).

2.3. BCS and milk production

2.4. Statistical analysis All statistical procedures were performed using SAS statistical system Package V9.1 (SAS, 2003). Univariate logistic regression model was fitted through Maximum Likelihood (ML) procedure to assess the effect of independent variable (NLP; categorized into four levels; D1 , D2 , D3 and D4 ), on the dependent variables: normal calving, calving difficulty and stillbirth. Reference category for the comparison of Crude Odds Ratios (CORs) was D2 . Results are expressed as percentages along with CORs and their 95% confidence interval [95% CI]. P-values of less than 0.05 were considered to indicate a statistically significant association with traits that were studied. The general linear model (GLM) procedure of SAS was used to analyze the repeatedly measured reproductive and production variables. The model for statistical analyses included the fixed effects of NLP length, genetic type and parity. The comparison of means was conducted using the Duncan’s multiple range tests, after verifying normality using Kolmogorov–Smirnov test. 3. Results 3.1. Incidence and COR for the effect of NLP length on calving traits Incidence and CORs for calving traits related to the NLP length in the current study were monitored from the

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Table 2 Incidence and CORs for the effect of the non-lactating period length on calving traits of different genetic types. Genetic type

Normal

Calving difficulty

Stillbirth

D1

D2

D3

D4

D1

D2

D3

D4

D2

D3

HO OR P-value

70.6 0.44 0.020

83.9 R –

83.3 0.93 0.843

72.1 0.49 0.041

19.5 2.23 0.034

11.5 R –

11.6 1.10 0.825

18.7 1.89 0.027

D1 9.8 1.74 0.302

4.53 R –

5.1 0.82 0.757

D4 9.1 1.54 0.424

BS OR P-value

76.9 0.69 0.463

82.3 R –

93.8 3.49 0.038

69.4 0.46 0.114

15.3 1.39 0.566

11.7 R –

3.8 0.31 0.015

19.4 1.83 0.284

7.6 1.36 0.696

5.8 R –

4.3 0.66 0.684

11.1 1.88 0.305

BF OR P-value

68.7 0.53 0.174

80.4 R –

85.7 2.26 0.021

53.8 0.29 0.007

18.7 1.34 0.586

13.1 R –

9.5 0.84 0.343

30.7 2.64 0.045

12.4 1.56 0.508

6.5 R –

4.7 0.73 0.674

10.3 2.19 0.227

Normal: Full term, easy or minimum assistance, but no calving difficulty, produces alive calf; Calving difficulty: difficult with veterinary assistance; Stillbirth: Calf was born dead, died during parturition or within 48 h of parturition. Non-lactating period length, D1 : <45 d; D2 : 45–60 d; D3 : 60–75 d; D4 : >75 d. COR: Odds ratio (95% CI); R: COR reference value (D2 ); HO: Purebred Holstein; BS: Purebred Brown Swiss; BF: F1 Crossbred Brown Swiss × Holstein cows.

second to the fifth parity (Table 2). The greater incidence of normal births in the purebred HO cows was recorded at D3 with no significant differences with D2 (83.3%; COR = 0.93) compared to differences of D1 and D4 NLP (70.6% and 72.1%; COR = 0.44 and 0.49, respectively). Meanwhile, there was a greater incidence of normal births with the purebred BS and BF cows that was recorded at D3 with significant differences with D2 (93.8% and 85.7%; COR = 3.49 and 2.26, respectively). The lesser incidence of calving difficulty in the purebred HO and BF cows was recorded at D3 with no significant differences with D2 (11.6% and 9.5%; COR = 1.10 and 0.84, respectively). However, the minimum incidence of calving difficulty in the purebred BS cows was at the same NLP length with significant differences with D2 (3.8%; COR = 0.31). The NLP length had no effect on the incidence of stillbirths in different genetic types.

and 328 d; 112 and 133 d, respectively). Furthermore, the greater indices of purebred BS and BF crossbred cows were prominent at extremely long NLP (D4 ).

3.3. Effect of NLP length on the subsequent milk production Data summarizing results for the effect of NLP length on subsequent milk production are included in Table 4. Purebred HO cows are noted for greater milk production ability; however, the current study revealed that there was a decrease in milk production parameters at either extremely short (D1 ) or long (D4 ) NLP lengths. Furthermore, the greater 305-MY of purebred HO cows was attained at the traditional NLP length (D2 , 8564 kg). However, the BF crossbred cows had decreased milk production at greater NLP lengths (D4 , 7440 kg). Purebred BS cows, however, were more durable from a structural integrity perspective and had consistent milk production considering all the NLP.

3.2. Effect of NLP length on the subsequent reproductive performance Data summarizing results for the effect of NLP length on the subsequent reproductive indices with different genetic types are included in Table 3. All reproductive indices of the purebred HO cows were decreased as the NLP length increased; however, days non-pregnant and average inseminations per parturition were similar (P > 0.05) at short (D1 ) and traditional (D2 ) NLP lengths (127 and 133 d; 3.81 and 3.64 d, respectively). Lesser estimates of calving interval and days non-pregnant in purebred BS and BF crossbred cows were recorded at longer (D3 ) NLP (350

3.4. Effect of NLP length on the subsequent BCS Data summarizing results for the effect of NLP length on the subsequent BCS were included in Table 4. Purebred HO and BF cows had a greater BCS at the extremely short (3.62 and 3.65, respectively) and long (3.59 and 3.71, respectively) NLP compared with the traditional NLP (45–60 d). Purebred BS cows, however, had no significant changes in BCS at different NLP.

Table 3 Effect of non-lactating period length on the subsequent reproductive measures of different genetic types (mean ± RSD). Genetic type

CI

DO

D1 HO BS BF

D2 d

381 394b 409b

D3 c

402 383b 377bc

D4 b

423 350b 328c

RSD a

454 427a 476a

38 36 35

AI

D1

D2 c

127 128b 156b

D3 bc

133 117b 138b

D4 b

140 112b 133b

RSD a

182 171a 189a

12 10 13

D1

D2 ab

3.81 3.19 3.65

D3 b

3.64 3.15 3.57

D4 a

4.08 3.14 3.44

CI, calving interval; DO, days non-pregnant; AI, average insemination per pregnancy. Dry period length, D1 : <45 d; D2 : 45–60 d; D3 : 60–75 d; D4 : >75 d. RSD: Residual standard deviation; HO: Purebred Holstein; BS: Purebred Brown Swiss; BF: F1 Crossbred Brown Swiss × Holstein cows. Values with different superscripts in each row are different at (P < 0.05).

RSD a

4.09 3.22 3.68

0.38 0.28 0.35

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Table 4 Effect of non-lactating period length on the subsequent BCS and milk yield of different genetic types (mean ± RSD). Genetic type

HO BS BF

BCS

305-MY

D1

D2

D3

D4

RSD

D1

D2

D3

D4

RSD

3.62a 2.89 3.65a

3.37b 2.85 3.47ab

3.45ab 2.83 3.24b

3.59a 2.96 3.71a

0.39 0.27 0.34

8206b 7331 8468a

8564a 7503 8669a

8370ab 7365 8647a

8166b 6981 7440b

659 588 677

BCS, body condition score; MY, milk yield. Non-lactating period length, D1 : <45 d; D2 : 45–60 d; D3 : 60 75 d; D4 : >75 d. RSD: Residual standard deviation; HO: Purebred Holstein; BS: Purebred Brown Swiss; BF: F1 Crossbred Brown Swiss × Holstein cows. Values with different superscripts in each row are different at (P < 0.05).

4. Discussion The primary objectives of the present study were to evaluate the effects of NLP length on the subsequent calving ease, reproductive and production performance of the purebred HO, BS and the F1 crosses of these breeds under subtropical conditions. The current study revealed that there was a lesser incidence of calving difficulty in the purebred HO and BF crossbred cows at the D2 and D3 NLP periods (45–60 and 60–75 d) and for the purebred BS cows was less at the D3 NLP (60–75 d). Similar to these results, there was a greater incidence of dystocia and retained placenta when there was a short NLP (35 d) similar to results reported previously for the purebred HO cows (Pezeshki et al., 2007). Atashi et al. (2013), however, concluded that dystocia was more frequent in cows with NLP periods of >60 d compared with those with shorter NLP; however, the rate of calving difficulty did not differ for cows with 51–60 d NLP compared with those with shorter NLP (P > 0.05). Furthermore, Enevoldsen and Sorensen (1992) reported that the risk of calving difficulty was greater in cows with 10wk NLP than in those with 7- or 4-wk NLP. The current study supports the concept that nutritional management strategies during the pre-partum period, along with NLP length, have an important role in reproductive status of dairy cows during the subsequent lactation. In the current study, the incidences of calving difficulty in the purebred HO, BS and the crosses of these breeds were comparable to that reported in the USA (Van Tassell et al., 2003; Cole et al., 2005). However, stillbirth rates were slightly greater than results from this previous study as recorded in the first, second and third parities (Cole et al., 2007). Consistent with the present results, Blöttner et al. (2011) reported a relatively lesser incidence of dystocia and stillbirths at the second and third calving. These variations could be attributed to managerial and environmental factors rather than having a genetic basis. All reproductive variables for the purebred HO cows were less desirable from a productivity perspective as the NLP length increased in the present study. However, the greater estimates of the purebred BS and BF crossbred cows were evident with extremely long NLP (D4 ). The superior indices in the purebred BS and BF crossbred cows may be attributed to the relatively symmetric BCS denoting the greater adaptability to frequent and sudden diet changes during the NLP. Moreover, it has been proven that changes in BCS affect the cow’s fertility (Butler and Smith, 1989; Garnsworthy and Webb, 1999). The less efficient reproductive status of purebred HO cows assigned to a NLP

of greater than 45-d may have contributed to the frequent and sudden changes in feed consumption during the NLP. Furthermore, such results in the purebred HO cows indicate that shortening the NLP in addition to making minimum changes in diet composition during the NLP could be an appropriate solution for improving reproduction in subsequent lactations. These findings support a recent study performed on purebred Holsteins and the backcrosses of this breed (El-Tarabany and El-Bayoumi, 2015). It was previously reported that days to first postpartum ovulation was 23.8 d for cows with a 28-d NLP compared with 31.9 d for cows with a 56-d NLP length (Gumen et al., 2005). Also, in this previous trial it was concluded that days nonpregnant were reduced when the NLP was shortened (93.8, 121.2, and 145.4 d for 0-, 28-, and 56-d NLP, respectively). This contrasts with the results of previous research where it was reported that there were fewer days that cows were not pregnant with a traditional (56-d) NLP than cows with a shorter NLP (Pezeshki et al., 2007). Nevertheless, in other studies it was found that the number of services, pregnancy rate, and days not pregnant did not differ when comparing short (30-d) to traditional (60-d) NLP (Lotan and Adler, 1976; Annen et al., 2004). Similarly, Pezeshki et al. (2007) did not detect a consistent improvement in reproductive measures with decreased NLP lengths, although first-service conception rate was greater in multiparous cows with a 35-d NLP compared with a 42- or 56-d NLP. The duration and the extent of the postpartum negative energy balance affect the fertility of dairy cows (Butler and Smith, 1989). Heinonen et al. (1988) reported poor reproductive performance in cows that lost more than 10% of body weight post-calving compared with those that lost a lesser percentage of body weight. Furthermore, Youden and King (1977) reported an effect of body weight change around the time of service on conception rate. Indirect indicators of energy balance status such as BCS are commonly used due to the difficulty of routinely measuring the energy balance status. Previous studies estimated the genetic correlations between fertility traits and BCS and suggested that cows with a genetically lesser BCS tend to have inferior fertility (Dechow et al., 2001; Pryce et al., 2004; Berry et al., 2003). The first postpartum ovulation occurred between 10 and 14 d after the energy balance nadir was reached, followed by resumption of estrous cycles (Butler et al., 1981; Canfield et al., 1990). However, reproductive performance of dairy cattle improved in other studies with an earlier return of estrous cycles (Darwash et al., 1997; Staples et al., 1990). Physiologically, a negative energy balance was associated with a delay in onset of ovarian activity

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by impinging on the pulsatile secretion of LH, the follicular responsiveness to LH, and eventually through limiting follicular estradiol production (Diskin et al., 2003). Beam and Butler (1997) concluded that follicles emerging during waves of ovarian follicular development after the negative energy balance nadir, rather than before had greater growth rates and attained a greater diameter, produced more estradiol, and there was a greater probability of ovulation occurring from the follicles. These results indicate that cows in a lesser BCS may not have been able to preserve energy in adequate amounts to activate ovarian function or exhibit estrus. From previous research, thinner cows at calving were more likely to have inactive ovaries or delayed resumption of corpus luteum function (Markusfeld et al., 1997; Reksen et al., 2002). Additionally, the 3-wk postpartum nonesterified fatty acid (NEFA) concentrations were less for cows with shorter than traditional NLP and this may reflect a more favorable energy balance (Watters et al., 2008). These types of cows are probably inseminated for the first time at a later date due to delay in the commencement of ovulation or estrus; however, the effect of BCS at calving on reproduction indices decreases with time postcalving (Markusfeld et al., 1997; Dechow et al., 2001). Evaluation of the cow’s condition should be carefully conducted. Body weight is of little relevance for the estimation of body fat mobilization stores because the fraction of body fat relative to body weight change varies to a great extent, depending on age and time since last feeding (Schröder and Staufenbiel, 2006). Additionally, the frame size of the animal must be observed as this impacts body weight and BCS. The BCS is a subjective measure and depends on the decision of the assessor. The current results for post-calving BCS changes in the purebred HO and BF crossbred cows confirmed that cows with shorter NLP experienced less negative energy balance than cows with longer NLP, perhaps because of greater feed intake. However, purebred BS cows had a more symmetric BCS indicating their greater adaptability during the frequent and sudden diet changes during the NLP. Similarly, reduction in BCS loss after parturition with shortened NLP has been reported by others (Farries and Hoheisel, 1989; Gulay et al., 2003). Rastani et al. (2005) found that post-calving BCS loss for the 56-d NLP group was greater than that of 28-d NLP group. Previous studies, however, demonstrated that BCS at calving was similar among experimental groups (28-d compared with 56-d and 30-d compared with 70-d NLP, respectively; Gulay et al., 2005). Gearhart et al. (1990) reported that cows losing body condition during the NLP were at greater risk of dystocia at the subsequent calving, with a 1-unit increase in BCS loss manifesting itself as 1.85 times greater odds for dystocia. Also, in this previous research it was concluded that one potential cause of the significant association between BCS change precalving and dystocia may be because of the herd manager attempting to achieve a target BCS at calving, thereby necessitating a reduction in BCS in cows that are in too great a BCS at the time of initiation of the NLP. In the current study, purebred HO cows, noted for great milk production ability, had a marked decrease in milk production parameters at extremely short (D1 ) and long (D4 ) NLP lengths. However, the BF crossbred cows had a lesser

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milk production with the longest NLP (D4 ). In contrast, purebred BS cows had a greater persistence and consistency of milk production at all NLP. Mammary involution and growth occur during the NLP and the rate of this process is an important factor for milk production efficiency in the subsequent lactation. Previous studies have shown that reducing the NLP length decreases milk yield in the subsequent lactation (Klusmeyer et al., 2009; Soleimani et al., 2010; Safa et al., 2013). This has also been proven in retrospective reports (Atashi et al., 2013; GhaviHossein-Zadeh and Mohit, 2013; Steeneveld et al., 2013). Furthermore, there was a 9.8% decrease in the relative contribution that the 30-d dry half udders made to the total daily amount of milk produced compared with half udders of the control group had 70-d NLP (Gulay et al., 2005). Jolicoeur et al. (2010), however, reported that shortening the NLP to 35 d augmented the milk yield by 3% compared with a NLP of 65 d. Other reports indicate that a shortening of the NLP had no effect on milk yield in the first 60 d postpartum (Soleimani et al., 2012; Cermakova et al., 2014). Accordingly, various rationales subsist for a decreased milk yield due to a short NLP. Schröder and Staufenbiel (2006) noted that a change in BCS during the first month of lactation has a greater impact on milk yield than BCS at parturition. Therefore, thinner cows produced more milk (Garnsworthy and Topps, 1982; Domecq et al., 1997). Excessive lipolysis has, however, been linked with the greater incidence of health disorders (e.g., fatty liver, ketosis, milk fever, and displaced abomasum) resulting in reduced milk yield (Grummer, 1993; Waltner et al., 1993; Rukkwamsuk et al., 1999). Mantovani et al. (2010) reported that cows without a NLP produced approximately 5.5 kg/d less milk and attained the peak of lactation 10 d earlier than cows appointed to a traditional NLP of 55 d. In contrast, Gulay et al. (2003) reported that a NLP of 30 d is adequate to sustain milk yield. However, other researchers reported a significant decrease in milk yield for second-lactation cows assigned to a short NLP, whilst yields from the third-or-greater lactation were not affected (Pezeshki et al., 2007; Watters et al., 2008; Santschi et al., 2011). These observations suggest that young cows are more liable to have a decrease in the NLP compared with older cows. This presumption has been confirmed in a retrospective study (Kuhn et al., 2006). Accordingly, it can be surmised that better milk yield of cows assigned to a traditional NLP was due to the greater numbers of active and functional mammary cells compared with cows with either short or long NLP (Capuco et al., 1997; Gulay et al., 2005). Furthermore, several hypotheses have been proposed that reduced milk production in cows experiencing a short NLP is due to a continuous influence of galactopoietic hormones or reduced mammary epithelial cell numbers or even abnormal cell turnover and replacement of senescent mammary epithelial cells during late gestation (Collier et al., 2012). In conclusion, decreasing reproductive efficiency in dairy herds has become an important economic concern. Improvements in reproductive efficiency lead to increased profit per cow and improved overall efficiency in dairy operations. The present study revealed that the minimum incidence of calving difficulty in the purebred HO and BF crossbred cows was reported at D2 (45–60 d) and D3

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(60–75 d) NLP. However, the purebred BS cows had a properly longer NLP (D3 , 60–75 d). All reproductive indices of the purebred HO cows decreased as the NLP length increased. However, the inferior reproductive indices of the purebred BS and BF crossbred cows were most pronounced with the longest NLP (D4 ). Purebred HO cows had less milk production at the shortest (D1 ) and longest (D4 ) NLP. However, purebred BS cows were persistent in amounts of milk produced and had a more consistent BCS and milk production at all NLP. These outcomes for the purebred HO cows indicate that shortening the NLP in addition to making minimum changes in diet composition during the NLP could be an appropriate solution for improving reproduction in subsequent lactations. Although the present study involves one of the first generation crosses, it is obvious that more generations are desired to completely evaluate the longterm differences in reproduction between purebred HO, BS and the crosses of these breeds. Conflict of interest statement The author has no conflict of interest to declare. Acknowledgement The author expresses the gratitude to Dr. Mohamed Afifi for his valuable and sincere efforts in statistical analysis. References Annen, E.L., Collier, R.J., McGuire, M.A., Vicini, J.L., 2004. Effects of dry period length on milk yield and mammary epithelial cells. J. Dairy Sci. 87, E66–E76. Atashi, H., Zamiri, M.J., Dadpasand, M., 2013. Association between dry period length and lactation performance, lactation curve, calf birth weight, and dystocia in Holstein dairy cows in Iran. J. Dairy Sci. 96, 3632–3638. Bachman, K.C., 2002. Milk production of dairy cows treated with estrogen at the onset of a short dry period. J. Dairy Sci. 85, 797–803. Bachman, K.C., Schairer, M.L., 2003. Invited review: bovine studies on optimal lengths of dry periods. J. Dairy Sci. 86, 3027–3037. Beam, S.W., Butler, W.R., 1997. Energy balance and ovarian follicle development prior to the first ovulation postpartum in dairy cows receiving three levels of dietary fat. Biol. Reprod. 56, 133–142. Berry, D.P., Buckley, F., Dillon, P., Evans, R.D., Rath, M., Veerkamp, R.F., 2003. Genetic relationships among body condition score, body weight, milk yield, and fertility in dairy cows. J. Dairy Sci. 86, 2193–2204. Blöttner, S., Heins, B.J., Wensch-Dorendorf, M., Hansen, L.B., Swalve, H.H., 2011. Brown Swiss × Holstein crossbreds compared with pure Holsteins for calving traits, body weight, back fat thickness, fertility, and body measurements. J. Dairy Sci. 94, 1058–1068. Butler, W.R., 2003. Energy balance relationships with follicular development, ovulation and fertility in postpartum dairy cows. Livest. Prod. Sci. 83, 211–218. Butler, W.R., Smith, R.D., 1989. Interrelationships between energy balance and postpartum reproductive function in dairy cattle. J. Dairy Sci. 72, 767–783. Butler, W.R., Everett, R.W., Coppock, C.E., 1981. The relationships between energy balance, milk production and ovulation in postpartum Holstein cows. J. Anim. Sci. 53, 742–748. Canfield, R.W., Sniffen, C.J., Butler, W.R., 1990. Effects of excess degradable protein on postpartum reproduction and energy balance in dairy cattle. J. Dairy Sci. 73, 2342–2349. Capuco, A.V., Akers, R.M., Smith, J.J., 1997. Mammary growth in Holstein cows during the dry period: quantification of nucleic acids and histology. J. Dairy Sci. 80, 477–485. Cermakova, J., Kudrna, V., Simeckova, M., Vyborna, A., Dolezal, P., Illek, J., 2014. Comparison of shortened and conventional dry period management strategies. J. Dairy Sci. 97, 5623–5636.

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