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Anim. Reprod., v.2, n.2, p.135-138, April/June, 2005 Feed intake restriction, conception rate and parturition to conception interval
in crossbred Gir-Holstein cows1
A.M. Ferreira2,5, W.F. Sá2, J.H.M. Viana2, L.S.A. Camargo2, P.A.C. Pereira3, C.A.C. Fernandes4
²Embrapa Dairy Cattle Research Center, R. Eugênio do Nascimento 610, Juiz de Fora, MG, ZC 36038-330 Brazil ³Federal University of Minas Gerais, Belo Horizonte, MG, Brazil 4Alfenas University, Alfenas, MG, Brazil Abstract
national dairy herds, 18 to 20 months according to studies carried out in Minas Gerais (Carneiro, 1992) and The purpose of this study was to evaluate the Rio de Janeiro (Ferreira et al., 1997), characterizes the effects of feed restriction and subsequent body weight low reproductive efficiency of herds associated with an loss on the number of services per conception in increased age at first parturition. crossbred, Gir-Holstein cows with body condition There are many possible causes of reproductive scores (BCS) ranging from 3.5 to 4.1 (1 = very thin and problems (Ferreira, 1985b) including but not limited to 5 = fat). The mean milk production during the first any disturbance or pathology that affects normal month of lactation was 11.9 kg/milk/day. Cows received reproductive function of heifers and/or cows and will be either a post-partum diet to meet maintenance and reflected by one of these symptoms: anestrous period production needs (Group I, n=25) or were submitted to (absence of estrous cycle and/or estrus); return to feed restriction from parturition to conception (Group II, service after AI or breed); and abortion (infectious or n=25), which consisted of 1 AU/ha of Brachiaria not), as described by Ferreira (1997). Wiltbank et al. decumbens pasture, during the dry season, without (1962) affirmed that cows that lost weight from concentrate supplementation. All animals were parturition to breeding had lower conception rates than inseminated in the first estrus 45 days post-parturition. Ovarian cyclic luteal activity (OCLA) was evaluated by those that had not (43% vs. 67%, respectively). Many rectal palpation, observation of estrous behavior (twice studies have shown that weight loss prior to breeding or daily) and blood progesterone levels. The difference in AI may reduce fertility (Perkins, 1985; Spicer et al, the interval from parturition to first estrus was greater in 1990; Pedron, 1993; Whitaker et al, 1993; Ferguson, the Group II (46.3 days) than Group I (55.4 days). In 1996), probably because follicles growing under a state conclusion, feed restriction and subsequent body weight of NEB may have lower quality due to the effects of loss (13.2%) did not retard the reestablishment of metabolic unbalance (Britt, 1992; 1994). OCLA in Gir-Holstein crossbred cows with a high BCS The purpose of the present study was to evaluate at parturition. The first estrus occurred before 56 days the effect of feed restriction and subsequent weight loss post-partum in the feed-restricted group and this group (implying a NEB) on the interval from parturition to had a greater number of services per conception and conception, the number of services per conception, and days to first service compared to the control group. service period length in Gir-Holstein cows with a high body condition score (BCS) at parturition. Keywords: Post-partum, feed restriction, services per
Materials and Methods
Introduction
Experimental Farm of Santa Mônica, in Valença, RJ, Reproductive performance is one of the main Brazil. Crossbred Gir-Holstein cows (n=50) with a factors affecting efficiency of dairy and beef herds BCS at parturition ranging from 3.5 to 4.1 (1 = very thin (Diskin et al., 2003). A negative energy balance (NEB), and 5 = fat; Ferreira, 1997) and mean milk production alters reproductive performance affecting age at puberty during the first month of lactation of 11.9 kg milk per (Kinder et al., 1995) and the duration of the post- day. Half of these cows received a post-partum diet to meet maintenance and production needs (Group I, parturition anestrous period (Dunne et al., 1999; n=25), and the other half (Group 2, n=25) was Sinclair et al., 2002). The low productivity of Brazilian submitted to feed restriction from parturition to dairy herds, considering milk production by area or by a conception and received a diet consisting of 1AU/ha of cow per year basis (Ferreira, 1991), is essentially related Brachiaria decumbens pasture during the dry season to: 1) low reproductive performance due to inadequate without concentrate supplementation to induce weight management (nutritional, sanitary and housing) and 2) loss. Parturitions occurred from March to April low genetic merit of cows (lactation yield, duration and (beginning of dry season), and all cows were length). The long calving interval observed in the inseminated at the first estrus 45 days post-partum. _________________________________________ 1Partially sponsored by FAPEMIG and CNPq 5Corresponding Author: ademirmf@cnpgl.embrapa.br Received: June 4, 2004 Accepted: July 8, 2005 Ferreira et al. Feed intake restriction, conception rate and parturition to conception interval in crossbred Gir-Holstein cows. Weight measurement and BCS evaluation were carried estrus for treatment groups are depicted in Table 1. The out 24h after parturition and weekly thereafter, in the mean live weight loss during this period was –6.0 and – morning, after milking, and before the feeding of Group 55.3 kg for Group I and II, respectively. Cows under I. Milk production was also assessed weekly after the feed restriction presented a loss of 0.9 units of BCS 10th day post-partum. Post-partum ovarian cyclic luteal between parturition and conception (mean of 3.8 at activity (OCLA) was evaluated weekly after Day 20 parturition and 2.9 at conception). Among the four post-partum by rectal palpation, twice-daily observation animals that lost the most weight from parturition to of estrous behavior, and by twice-weekly blood- first estrus (14.6 to 14.9%), estrus occurred 50 to 71 progesterone levels. Blood samples were collected by coccigeal tail vein or artery puncture, using Vacutainer There was no difference (P>0.05) in interval heparinized tubes. Plasma was separated by parturition to first estrus between Groups I and II, but centrifugation at 484.4g for 20 minutes under service periods for these groups were different refrigeration (4 oC) and stored at -20 oC. Progesterone (74.7±17.7 vs. 114.6±15.7 days, respectively; P<0.001). concentrations were measured by radioimmunoassay, using a commercially available I125 solid-phase RIA The number of services per conception in the group Kit (Coat-a-Count, MedLab, Brazil), with a sensitivity under feed restriction was higher compared to control of 0.03 ng/mL, and intra- and interassay coefficients of variation of 0.57% and 6.42%, respectively. The percentage of unidentified estruses for the The percentage of observed estruses in each Ferreira et al. Feed intake restriction, conception rate group was evaluated by the Chi-square method. All and parturition to conception interval in crossbred Gir-other parameters compared by Student´s T test, Holstein cows group under feed restriction was 39.51%, considering a significance level P<0.05. Data is not different from the 36.3% observed in the control presented as means ± standard deviation. group (P>0.05). There was no difference (P>0.05) in progesterone levels for the two groups studied (4.9±3.2 and 5.1±2.6 ng/mL for Groups I and II, respectively) during the estrous cycles before and after the AI Means of the interval from parturition to first Table 1. Effect of feed restriction from parturition to conception on reproductive parameters of Gir-Holstein cows Interval from parturition to 1st estrus (days) Unidentified estrus or ovulations without estrus WLRP = Mean weight loss related to weight at parturition (kg and %). DWL= Mean weight loss by day (kg). a,b Values followed by different letters, in the same row, differ (P<0.01). Anim. Reprod., v.2, n.2, p.135-138, April/June, 2005 Ferreira et al. Feed intake restriction, conception rate and parturition to conception interval in crossbred Gir-Holstein cows. Discussion
Ferguson (1996), cows can tolerate the loss of 0.67 units of BCS without affecting fertility. However, Perkins The mean weight loss of 11.8% from (1985) and Britt (1992) affirmed that cows losing more parturition to first estrus was not sufficient to increase than 0.5 units of BCS had a reduction in conception the time to 1st estrus past the desired period of 85 days rate, in agreement with the results of the present post-parturition, considering a 12 month calving experiment. interval. These results are in agreement with those of Harris (1993) and Ruegg and Milton (1995) Rhodes et al. (1995; 1996), Bossis et al. (1999), Stagg stated that fertility is affected when animals lost more (2000) and Diskin et al. (2003), which showed that than 1.0 units of BCS post-parturition but did not cows started an anestrous condition when the average mention the BCS at parturition. Pedron (1993) however loss of initial body weight was around 22 to 24%. A low mentioned that a loss of 0.8 and 1.05 units of BCS for BCS at the beginning of feed restriction may be one of cows with scores of 3.5 and 4.0 soon after parturition, the factors that affected the interval to anestrus (Diskin respectively, did not affect service period and the et al., 2003). For this reason, cows used in the present number of services per conception. This inconsistency study were selected for a high BCS at parturition. between the current and previous studies may be The length of service periods for Groups I and explained by the different numeric values attributed to II were different and may be related to the higher the BCS systems used between experiments. The former number of services per conception in the group under authors defined fat cows as presenting a BCS of 4.0, and feed restriction. Lower conception rates associated with very fat cows as 5.0, while in the present study the same follicles, which grew under a NEB, may be due to an grades of BCS were attributed, respectively. effect of a metabolic imbalance on oocyte or follicle Furthermore, our study deals with cows with higher (Britt, 1992 and 1994). Ferguson (1996) also suggested milk production potential, and capable of mobilizing that cows in a NEB had lower conception rates. The more fat from internal stores at the beginning of higher number of services per conception for the group lactation which is less evident in BCS evaluation. There under feed restriction might explain the difference of is also the fact that BCS evaluation, although being an 39.9 days in service period between the two groups. efficient auxiliary technique for nutritional, Differences in estrus detection rate may be a reproductive, and health management is subjective, consequence of animals under feed restriction having which can result in variations in scoring (Ferguson et lower expression or intensity of estrus behavior al., 1994; Hady et al., 1994). (Ferreira, 1990; Ferguson, 1996). The causes of silent or When considering the rate of return to estrus in undetected estruses in relation to a NEB have been Gir-Holstein crossbred cows after breeding or AI, discussed by Spicer et al. (1990) who verified that 40% weight loss or a NEB should be considered as possible of first post-partum ovulations were not associated with causes of repeat breeder syndrome, as occurs with heat estrus in cows under NEB, when compared to 16.7% of stress (Gonzalez et al., 1993; Valtorta and Gallardo, 1996). those under positive energy balance (PEB). However, Appropriate attention must be given to these two factors these latter authors observed no difference in the along with many other possible causes when diagnosing interval from parturition to first estrus for cows under low reproductive performance (Ferreira, 1985a). either PEB or NEB, which is also in agreement with the In summary, for Gir-Holstein cows kept under results of the present study. Pedroso and Roller (1997) post-partum feed restriction and with a high BCS, the also mentioned the occurrence of silent estrus or mean live weight loss of 11.7 and 13.2% from ovulation without visible signs of estrus in animals parturition to first estrus and to conception, respectively, under feed restriction. did not affect the interval from parturition to first estrus Another factor that could explain the lower interval while the number of services per conception conception rate of cows under feed restriction is the lower level of progesterone produced by the corpus luteum of cows under a NEB (Britt, 1994). Spicer et al. References
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