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Grazing behavior of drylot-developed beef heifers and the influence of postinsemination supplementation on artificial-insemination pregnancy success
The Professional Animal Scientist 31 (2015):264–269; http://dx.doi.org/10.15232/pas.2014-01374 ©2015 American Registry of Professional Animal Scientists
Grazing behavior of drylotdeveloped beef heifers and the influence of postinsemination supplementation on artificialinsemination pregnancy success G. A. Perry,1 PAS, E. L. Larimore, B. L. Perry, and J. A. Walker Department of Animal Science, South Dakota State University, Brookings 57007
ABSTRACT Research has indicated that moving drylot-developed heifers to spring forage immediately after AI adversely affects ADG and AI conception rates. Our objective was to determine the effect of adaption to grazing on ADG and activity, and whether post-AI supplementation would improve AI pregnancy success. In Exp. 1, heifers were developed in a single pen. At the start of treatment (d −44) heifers were blocked by BW and either remained in the drylot (DLT; n = 34) or were moved to forage (GRS; n = 35). Pedometers were placed on 5 heifers per treatment on d −19. On d 0, DLT heifers were moved to forage. Heifers on GRS had decreased (P < 0.01) ADG from d −44 to −35 compared with DLT heifers. Following being moved (d 0) DLT heifers had decreased (P < 0.01) ADG compared with GRS heifers. Initially, GRS heifers took more (P < 0.05) steps, but after
1 Corresponding author: george.perry@ sdstate.edu
being moved, DLT heifers took more (P < 0.05) steps from d 0 to 3. In Exp. 2, drylot-developed heifers (n = 301) at 2 locations were synchronized with the 7-d CIDR protocol. At AI, heifers were randomly assigned within location to be either moved to pasture or moved to pasture plus being supplemented. Pregnancy success was affected by treatment (P = 0.02), with supplemented heifers having improved pregnancy success. In summary, moving drylot-developed heifers to forage affected performance and activity, but supplementation when moved to pasture at AI improved pregnancy success. Key words: fertility, grazing behavior, heifers, post–artificial insemination nutrition
INTRODUCTION The United States beef and dairy industries are affected by reproductive failure, with costs totaling approximately $1 billion annually (Bellows, et al., 2002), and the economic value of reproduction is 5 times greater than
calf growth for commercial beef producers (Trenkle and Willham, 1977). Research has indicated that moving drylot-developed heifers to spring forage immediately after AI adversely affects ADG and AI conception rates (Perry et al., 2013). However, after 27 d of grazing there was no difference in ADG between heifers developed in a drylot and heifers developed on forage (Perry et al., 2013). Grazing skills and dietary habits are learned early in life (Provenza and Balph, 1988). This learning is important to the development of motor skills necessary to harvest and ingest forages (Provenza and Balph, 1987), and they allow animals to increase their consumption of forage (Lyford, 1988). These skills, acquired between weaning and breeding, are carried through to the next grazing season (Olson et al., 1992). Nutritionally mediated changes to the uterine environment can occur by changing components of uterine secretions or by influencing the circulating concentrations of progesterone that regulate the uterine environment
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(Foxcroft, 1997). Hill et al. (1970) reported decreased embryonic growth among heifers fed 85% maintenance requirements of energy and protein on d 3 and 8 after insemination compared with heifers fed 100% maintenance. Therefore, undernutrition immediately following insemination can have an effect on embryo survival and the ability of heifers to conceive or maintain a pregnancy during a defined breeding season. The objectives of these experiments were to determine the effect of adaption to grazing on BW change and activity when heifers were moved to spring forage (Exp. 1) and whether supplementing heifers moved to pasture following AI improved pregnancy success (Exp. 2).
MATERIALS AND METHODS The South Dakota State University Animal Care and Use Committee approved all procedures.
Exp. 1 Experimental Design. Anguscross beef heifers were developed in a single pen following weaning until 14 mo of age. At the start of treatment (d −44) heifers were blocked by BW and allotted to 1 of 2 treatments. Heifers either remained in the drylot (DLT; n = 34) or were moved to spring forage (GRS; n = 35). Body weights were collected on d −44, −35, −24, −3, 9, and 30. All heifers were moved to feedlot pens without feed for >12 h before being weighed. Pedometers (IceCubes by IceRobotics, Edinburgh, Scotland) were placed on 5 heifers per treatment on d −19 to determine number of steps and amount of time standing or lying. Days in which GRS heifers were brought from the pasture to the working facilities were removed from the data set before analysis. Heifers in DLT remained in a single drylot pen from d −19 to 0. However, to maintain normal grazing management, GRS heifers were moved to a new pasture on d −9. On d 0 GRS heifers were moved to a new pas-
ture, and DLT heifers were moved to spring forage but were maintained separate from GRS heifers (~12.1 ha per group). Primary grasses within these pastures were smooth brome (Bromus inermis), quackgrass (Elytrigia repens), and Kentucky bluegrass (Poa pratensis). The period of time when heifers were being moved to pasture was removed from pedometer data set, and data were analyzed as activity in each 24-h period following when heifers were moved to pasture. All heifers were synchronized with the prostaglandin (PG) 6-d CIDR (controlled internal drug-releasing device) protocol, which included an injection of PGF2α (25 mg as 5 mL of Lutalyse i.m.; Pfizer Animal Health, New York, NY) on d −12, an injection of gonadotropin-releasing hormone (GnRH; 100 μg as 2 mL of Cystorelin i.m.; Merial, Athens, GA) and insertion of a CIDR (Pfizer Animal Health) on d −9, a PGF2α injection and CIDR removal on d −3, and an injection of GnRH on d 0 for all heifers. Statistical Analysis. For each treatment evaluated, animal was used as the experimental unit because the treatment applied was movement to a grazing situation and was applied to each individual animal. In addition, there was sufficient forage present in the pastures, and all animals were allowed to freely move around each pasture and were allowed to consume ad libitum intake. The effects of adaption to grazing on ADG, number of steps taken, and amount of time standing or lying were analyzed by ANOVA for repeated measures using the MIXED procedures (SAS Institute Inc., Cary, NC) as described by Littell et al. (1998). All covariance structures were modeled in the initial analysis; indicated best-fit covariance structure for BW was compound symmetry, anteindependent for ADG, and heterogeneous compound symmetry for pedometer data and were used for the final analysis. The model included the independent variables of treatment, day, and treatment × day. When a significant (P ≤ 0.05) effect of treatment, day, or treatment × day
was detected, least squares means were separated by the Pdiff option (SAS Institute Inc.).
Exp. 2 Experimental Design. Anguscross beef heifers (n = 301) at 2 locations were developed within location as a single group from weaning until AI on a corn-silage concentrate diet. At time of AI, heifers were randomly assigned to 1 of 2 treatments: (1) moved to pasture (RNG) or (2) moved to pasture and supplemented with 2.2 kg per heifer per day of dried distillers grains plus solubles for 42 d (RNG-SUPP). Forage biomass and nutrient compositions were determined when heifers were moved to pastures (d 0; Table 1). Biomass was determined by clipping useable forage at a height of 2.54 cm within a 0.96m2 loop. Forage samples were weighed and dried, and DM forage was calculated (Table 1). Primary grasses at location 1 were smooth brome (Bromus inermis), quackgrass (Elytrigia repens), and Kentucky bluegrass (Poa pratensis). Primary grasses at location 2 were smooth brome (Bromus inermis), big bluestem (Andropogon gerardi), quackgrass (Elytrigia repens), and Kentucky bluegrass (Poa pratensis). All heifers were synchronized with an injection of GnRH (100 μg i.m. as 2 mL of Cystorelin i.m.; Merial) and insertion of a CIDR device and 7 d later an injection of PGF2α (25 mg i.m. as 5 mL of Lutalyse i.m.; Pfizer Animal Health) at time of CIDR removal. At location 1 (n = 143; 406.9 ± 3.1 kg), estrus detection was done with the aid of EstroTect (Western Point Inc., Apple Valley, MN) estrusdetection aids, and approximately 12 h following the initiation of standing estrus, heifers were inseminated by 1 of 3 technicians to a single sire. Heifers not detected in estrus were inseminated at 72 h after CIDR removal with an injection of GnRH (100 μg i.m.) concurrent with insemination. An equal number of heifers inseminated at 72 h with GnRH were assigned
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Table 1. Nutrient composition and quantity of forage biomass at time of heifer turnout for each location1 Location 1 Item DM, % CP, % TDN, % ADF, % NDF, % Forage DM, kg/ha
Location 2
RNG
RNG-SUPP
RNG
RNG-SUPP
57 15.9 67 30 52.2 2,173
48 13.8 62 34.2 51.4 1,278
55 10.3 63 37 60.9 1,894
40 8.7 60 41.9 65.5 985
At time of AI, heifers were randomly assigned to 1 of 2 treatments: (1) moved to pasture (RNG) or (2) moved to pasture and supplemented with 2.22 kg per heifer per day of dried distillers grains plus solubles (24% CP) for 42 d (RNG-SUPP).
1
to each treatment. At location 2 (n = 158; 432.4 ± 3.2 kg), all animals were inseminated 54 h after CIDR removal by one technician to 1 of 2 sires. An injection of GnRH (100 μg i.m.) was given concurrent with insemination. Following insemination, heifers were immediately placed in their treatment group and remained in treatment groups until pregnancy was determined by transrectal ultrasonography on d 42. Bulls were placed with heifers 14 d following the final AI for the remainder of the breeding season (30 d at location 1 and 60 d at location 2). Artificial-insemination conception rates were determined by transrectal ultrasonography on d 42. Breeding-season pregnancy rates were determined 30 to 50 d after bulls were removed at each location. Statistical Analysis. Given the binary nature of the data, if one animal consumed more than their share of the supplement and another animal consumed less, the benefit to the animal consuming more (i.e., pregnant) would be canceled out by the decreased intake of the other animal (i.e., not pregnant). Thus, each individual animal was used as the experimental unit, and pregnancy data were analyzed using the GLIMMIX procedure (SAS Institute Inc.). The model included treatment, sire, location, BCS at AI, and the treatment × location interaction. When a significant (P ≤ 0.05) effect was detected, least
squares means were separated by the Pdiff option (SAS Institute Inc.).
RESULTS AND DISCUSSION Exp. 1 There was a treatment (P < 0.01), day (P < 0.01), and a treatment × day (P < 0.01) interaction on ADG (Figure 1). Heifers on GRS had decreased (P < 0.01) ADG from d −44 to −35 compared with DLT heifers. There was no difference between treatments in ADG from d −35 to −19 or from d −19 to −3. Following being moved to spring forage, DLT heifers had decreased (P < 0.01) ADG from d −3 to 9 and from d 9 to 30 compared with GRS heifers. In this experiment, naïve (DLT) heifers lost BW compared with heifers that had an adaption period to grazing. This loss in BW was similar to previous reports when heifers were moved to a spring grazing situation after being developed in a drylot from weaning to breeding (Perry et al., 2013). From d −19 to −6, there was an effect of treatment (P < 0.01), day (P < 0.01), and a treatment × day (P = 0.03) interaction on the number of steps taken each day (Figure 2), with GRS heifers taking more (P < 0.05) steps per day than DLT heifers. Following being moved to spring forage, DLT heifers took more (P <
0.05) steps per day on d 0, 1, 2, and 3 compared with GRS heifers (Figure 3). This increase in activity was similar to dairy heifers that did not have prior grazing experience compared with heifers that had previously grazed pastures (Lopes et al., 2013). However, across the entire experiment there was no treatment effect on the amount of time a heifer spent standing or lying per day. Therefore, DLT heifers took more steps in the same amount of time as the GRS heifers, which means more time was spent investigating the new environment and less time was spent grazing by the DLT heifers. The majority of grazing behavior is learned when an animal transitions from maternal care to independence (Provenza and Balph, 1988); this learning results in the development of the motor skills necessary to harvest and ingest forages efficiently (Provenza and Balph, 1987). Furthermore, the willingness to try novel food declined as an animal aged (Provenza and Balph, 1988). Thus livestock usually ingest small amounts of novel food and gradually increase the amount ingested if no adverse effects occur (Chapple and Lynch, 1986; Burritt and Provenza, 1987). When introduced to novel food or environment, livestock may spend more time and energy foraging (Osuji, 1974) but ingest less food (Arnold and Maller, 1977; Hodgson and Jamieson, 1981; Curll and Davidson, 1983). When dairy heifers that had been developed in confinement were moved to pasture, it took 5 d for them to develop a similar grazing pattern as experienced animals (Lopes et al., 2013). Similarly, in this experiment 5 d after being moved to pasture, DLT heifers took a similar number of steps as GRS heifers. However, ADG was decreased for 30 d after being moved to pasture. This decrease is similar to the report of Perry et al. (2013), where inexperienced heifers had decreased ADG compared with experienced heifers for the first 27 d after being moved to grazing.
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Exp. 2
Figure 1. Average daily gain (means ± SE) for heifers in Exp. 1. Heifers on GRS were moved from the drylot to forage on d −44, and DLT heifers were moved from the drylot to forage on d 0. **P < 0.01 within day.
Figure 2. Number of steps taken per day (means ± SE) from d −19 to −6 of treatments in Exp. 1. Heifers on GRS were moved from the drylot to forage on d 0. Heifers on GRS were moved to a new pasture on d −9 and 0. Heifers in DLT were still in the drylot (P < 0.05). Days that GRS heifers were moved to the working facilities for collection of weight data or synchronization were removed from the data analysis (d −14 and −13).
Forage quality within each of the pastures had adequate CP and energy to allow BW gain of animals (Table 1), based on nutrient recommendations (NRC, 2000). Additionally, available forage biomass was not limiting consumption using an average consumption rate of 12 kg per heifer per day for a 454-kg animal unit (Smart et al., 2010). Hence, all groups of animals in Exp. 2 had enough forage available and excess nutrients required for BW gain when moved to grass. However, conception rates to AI were affected by treatment (P = 0.02), with RNG-SUPP heifers having increased pregnancy success compared with RNG heifers (76 ± 7.5% and 61 ± 9.7%, respectively). There was no effect of location (P = 0.64), or treatment by location (P = 0.21), or BCS at AI (P = 0.40) on AI conception rates. Breeding-season pregnancy rates were not different (P = 0.20) between RNG and RNG-SUPP heifers (91 ± 3.4% and 94 ± 2.4%, respectively). Undernourishment due to lack of feed availability or poor-quality feed has been reported to be detrimental to reproductive functions and efficiency (Diskin et al., 2003). In this experiment, animals were not undernourished based on forage nutrient analysis, and based on this analysis animals consuming 2% of BW would gain >0.45 kg/d. However, if animal activity increased (as reported in Exp. 1) and animals did not consume sufficient forage, this situation could cause a short period of undernourishment, possibly affecting AI conception rates. Heifers on RNG-SUPP consumed dried distillers grains plus solubles at an average rate of 2.22 kg per heifer per day, supplying 0.66 kg of CP and 4.8 Mcal of supplemental nutrients. If RNG-SUPP consumed 3.0 kg of forage DM, the animals would have met their nutrient requirement for 0.22 kg/d of BW gain; however, the nutrients of the RNG heifers were acquired from only forage, and they would have had to consume 5.8 kg of DMI/d to meet the same BW-gain goal. A
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ent intake and increased activity as unexperienced heifers took more steps daily compared with adapted heifers. Supplementing heifers when they were moved to a forage grazing situation resulted in improved AI conception rates compared with moving heifers to a pasture without supplementation. Therefore, when heifers are developed in a drylot situation, high AI conception rates are possible, but management decisions need to be considered to avoid allowing heifers to enter a negative energy balance immediately following AI.
IMPLICATIONS Figure 3. Number of steps taken per day (means ± SE) from d 0 to 8 of treatment in Exp. 1. Heifers on GRS were moved from the drylot to forage on d −44. Heifers in DLT were moved from the drylot to forage on d 0. *P < 0.05.
decrease in feed intake from 120% of maintenance to 40% of maintenance resulted in a BW loss of 1.83 kg/d for a 2-wk period, and the majority of heifers stopped having normal estrous cycles (Mackey et al., 1999). Heifers fed only 85% maintenance requirements of energy and protein had reduced embryo development on d 3 and 8 after insemination compared with heifers fed 100% maintenance (Hill et al., 1970). Pregnancy establishment is dependent on oviductal and uterine secretions (Spencer and Bazer, 2004), including nutritional factors that are required for embryo growth and survival (Gao et al., 2009; Block et al., 2011). This decrease in energy intake could have a direct effect on changing the uterine environment by changing components of uterine secretions or an indirect effect by influencing the circulating concentrations of progesterone that regulate the uterine environment (Foxcroft, 1997). Hill et al. (1970) observed an immediate reduction in corpus luteum size and circulating concentrations of progesterone in heifers exposed to nutrient restriction. However, neither Spitzer et al. (1978) nor Rhodes et al. (1995) reported a difference in circulating concentrations of proges-
terone in heifers following nutrient restriction. A decrease in nutrient intake, as determined by ADG, when drylot-developed heifers were moved to a grazing situation immediately following insemination resulted in decreased AI conception rates (Perry et al., 2013). In this experiment, supplementing drylot-developed heifers for 42 d following insemination resulted in improved AI conception rates compared with heifers that were not supplemented. It was not determined what duration of supplementation was needed to increase pregnancy success. The duration of 42 d was used to keep heifers on a positive level of nutrition until pregnancy determination. In addition, by this point of pregnancy the fetus is completely attached to the uterus (Fléchon and Renard, 1978) and incidence of embryonic mortality is reduced. Research from our laboratory has indicated that after 27 d of grazing, ADG is similar between heifers developed on range and heifers developed in a drylot (Perry et al., 2013). In summary, following being moved to spring forage, drylot-developed heifers had decreased ADG compared with heifers that had prior grazing experience. This decrease in ADG is likely because of decreased nutri-
Achieving optimal AI conception rates with heifers developed in drylots requires management that avoids negative BW loss immediately following AI. Management options include (1) adaption to grazing before AI, (2) supplementation for animals while on pasture for approximately 30 d, or (3) retention of heifers in drylot until after AI.
ACKNOWLEDGMENTS This research was supported by the South Dakota Agricultural Experiment Station and the South Dakota Corn Utilization Council. Mention of a proprietary product does not constitute a guarantee or warranty of the product by South Dakota Agricultural Experiment Station or the authors and does not imply its approval to the exclusion of other products that may also be suitable. The authors gratefully acknowledge Pfizer Animal Health for their contribution of CIDR and Lutalyse and S. Fields, J. Krantz, J. Nelson, and C. Wright at South Dakota State University for their technical assistance.
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Chapple, R. S., and J. J. Lynch. 1986. Behavioral factors modifying acceptance of supplementary foods by sheep. Res. Dev. Agric. 3:113–120.
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Curll, M. L., and J. L. Davidson. 1983. Defoliation and productivity of a Phalarissubterranean clover sward, and the influence of grazing experience on sheep intake. Grass Forage Sci. 38:159–167. Diskin, M. G., D. R. Mackey, J. F. Roche, and J. M. Sreenan. 2003. Effects of nutrition and metabolic status on circulating hormones and ovarian follicle development in cattle. Anim. Reprod. Sci. 78:345–370. Fléchon, J. E., and J. P. Renard. 1978. A scanning electron microscope study of the hatching of bovine blastocysts in vitro. J. Reprod. Fertil. 53:9–12. Foxcroft, G. R. 1997. Mechanisms mediating nutritional effects on embryonic survival in pigs. J. Reprod. Fertil. Suppl. 52:47–61. Gao, H., G. Wu, T. E. Spencer, G. A. Johnson, X. Li, and F. W. Bazer. 2009. Select nutrients in the ovine uterine lumen. I. Amino acids, glucose, and ions in uterine lumenal flushings of cyclic and pregnant ewes. Biol. Reprod. 80:86–93. Hill, J. R., Jr., D. R. Lamond, D. M. Henricks, J. F. Dickey, and G. D. Niswender.
Lyford, S. J., Jr. 1988. Growth and development of the ruminant digestive system. Pages 44–63 in The Ruminant Animal. D. C. Church, ed. Prentice Hall, Englewood Cliffs, NJ. Mackey, D. R., J. M. Sreenan, J. F. Roche, and M. G. Diskin. 1999. Effect of acute nutritional restriction on incidence of anovulation and periovulatory estradiol and gonadotropin concentrations in beef heifers. Biol. Reprod. 61:1601–1607. NRC. 2000. Nutrient Requirements of Beef Cattle. 7th rev. ed. Natl. Acad. Press, Washington, DC. Olson, K. C., J. R. Jaeger, and J. R. Brethour. 1992. Growth and reproductive performance of heifers overwintered in range or drylot environments. J. Prod. Agric. 5:72–76. Osuji, P. O. 1974. The physiology of eating and the energy expenditure of the ruminant at pasture. J. Range Manage. 27:437–443. Perry, G. A., B. L. Perry, J. A. Walker, C. L. Wright, R. R. Salverson, and H. H. Patterson. 2013. Evaluation of prior grazing experience
269 on reproductive performance in beef heifers. Prof. Anim. Sci. 29:595–600. Provenza, F. D., and D. F. Balph. 1987. Diet learning by domestic ruminants: theory, evidence and practical Implications. Appl. Anim. Behav. Sci. 18:211–232. Provenza, F. D., and D. F. Balph. 1988. Development of dietary choice in livestock on rangelands and its implications for management. J. Anim. Sci. 66:2356–2368. Rhodes, F. M., L. A. Fitzpatrick, K. W. Entwistle, and G. Death. 1995. Sequentialchanges in ovarian follicular dynamics in Bos indicus heifers before and after nutritional anestrus. J. Reprod. Fertil. 104:41–49. Smart, A. J., J. D. Derner, J. R. Hendrickson, R. L. Gillen, B. H. Dunn, E. M. Mousel, P. S. Johnson, R. N. Gates, K. K. Sedivec, K. R. Harmoney, J. D. Volesky, and K. C. Olson. 2010. Effects of grazing pressure on efficiency of grazing on North American Great Plains rangelands. Rangeland Ecol. Manag. 63:397–406. Spencer, T. E., and F. W. Bazer. 2004. Uterine and placental factors regulating conceptus growth in domestic animals. J. Anim. Sci. 82(E-Suppl.):E4–13. Spitzer, J. C., G. D. Niswender, G. E. Seidel Jr., and J. N. Wiltbank. 1978. Fertilization and blood levels of progesterone and LH in beef heifers on a restricted energy diet. J. Anim. Sci. 46:1071–1077. Trenkle, A., and R. L. Willham. 1977. Beef production efficiency. Science 198:1009– 1015.
Grazing behavior of drylotdeveloped beef heifers and the influence of postinsemination supplementation on artificialinsemination pregnancy success G. A. Perry,1 PAS, E. L. Larimore, B. L. Perry, and J. A. Walker Department of Animal Science, South Dakota State University, Brookings 57007
ABSTRACT Research has indicated that moving drylot-developed heifers to spring forage immediately after AI adversely affects ADG and AI conception rates. Our objective was to determine the effect of adaption to grazing on ADG and activity, and whether post-AI supplementation would improve AI pregnancy success. In Exp. 1, heifers were developed in a single pen. At the start of treatment (d −44) heifers were blocked by BW and either remained in the drylot (DLT; n = 34) or were moved to forage (GRS; n = 35). Pedometers were placed on 5 heifers per treatment on d −19. On d 0, DLT heifers were moved to forage. Heifers on GRS had decreased (P < 0.01) ADG from d −44 to −35 compared with DLT heifers. Following being moved (d 0) DLT heifers had decreased (P < 0.01) ADG compared with GRS heifers. Initially, GRS heifers took more (P < 0.05) steps, but after
1 Corresponding author: george.perry@ sdstate.edu
being moved, DLT heifers took more (P < 0.05) steps from d 0 to 3. In Exp. 2, drylot-developed heifers (n = 301) at 2 locations were synchronized with the 7-d CIDR protocol. At AI, heifers were randomly assigned within location to be either moved to pasture or moved to pasture plus being supplemented. Pregnancy success was affected by treatment (P = 0.02), with supplemented heifers having improved pregnancy success. In summary, moving drylot-developed heifers to forage affected performance and activity, but supplementation when moved to pasture at AI improved pregnancy success. Key words: fertility, grazing behavior, heifers, post–artificial insemination nutrition
INTRODUCTION The United States beef and dairy industries are affected by reproductive failure, with costs totaling approximately $1 billion annually (Bellows, et al., 2002), and the economic value of reproduction is 5 times greater than
calf growth for commercial beef producers (Trenkle and Willham, 1977). Research has indicated that moving drylot-developed heifers to spring forage immediately after AI adversely affects ADG and AI conception rates (Perry et al., 2013). However, after 27 d of grazing there was no difference in ADG between heifers developed in a drylot and heifers developed on forage (Perry et al., 2013). Grazing skills and dietary habits are learned early in life (Provenza and Balph, 1988). This learning is important to the development of motor skills necessary to harvest and ingest forages (Provenza and Balph, 1987), and they allow animals to increase their consumption of forage (Lyford, 1988). These skills, acquired between weaning and breeding, are carried through to the next grazing season (Olson et al., 1992). Nutritionally mediated changes to the uterine environment can occur by changing components of uterine secretions or by influencing the circulating concentrations of progesterone that regulate the uterine environment
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(Foxcroft, 1997). Hill et al. (1970) reported decreased embryonic growth among heifers fed 85% maintenance requirements of energy and protein on d 3 and 8 after insemination compared with heifers fed 100% maintenance. Therefore, undernutrition immediately following insemination can have an effect on embryo survival and the ability of heifers to conceive or maintain a pregnancy during a defined breeding season. The objectives of these experiments were to determine the effect of adaption to grazing on BW change and activity when heifers were moved to spring forage (Exp. 1) and whether supplementing heifers moved to pasture following AI improved pregnancy success (Exp. 2).
MATERIALS AND METHODS The South Dakota State University Animal Care and Use Committee approved all procedures.
Exp. 1 Experimental Design. Anguscross beef heifers were developed in a single pen following weaning until 14 mo of age. At the start of treatment (d −44) heifers were blocked by BW and allotted to 1 of 2 treatments. Heifers either remained in the drylot (DLT; n = 34) or were moved to spring forage (GRS; n = 35). Body weights were collected on d −44, −35, −24, −3, 9, and 30. All heifers were moved to feedlot pens without feed for >12 h before being weighed. Pedometers (IceCubes by IceRobotics, Edinburgh, Scotland) were placed on 5 heifers per treatment on d −19 to determine number of steps and amount of time standing or lying. Days in which GRS heifers were brought from the pasture to the working facilities were removed from the data set before analysis. Heifers in DLT remained in a single drylot pen from d −19 to 0. However, to maintain normal grazing management, GRS heifers were moved to a new pasture on d −9. On d 0 GRS heifers were moved to a new pas-
ture, and DLT heifers were moved to spring forage but were maintained separate from GRS heifers (~12.1 ha per group). Primary grasses within these pastures were smooth brome (Bromus inermis), quackgrass (Elytrigia repens), and Kentucky bluegrass (Poa pratensis). The period of time when heifers were being moved to pasture was removed from pedometer data set, and data were analyzed as activity in each 24-h period following when heifers were moved to pasture. All heifers were synchronized with the prostaglandin (PG) 6-d CIDR (controlled internal drug-releasing device) protocol, which included an injection of PGF2α (25 mg as 5 mL of Lutalyse i.m.; Pfizer Animal Health, New York, NY) on d −12, an injection of gonadotropin-releasing hormone (GnRH; 100 μg as 2 mL of Cystorelin i.m.; Merial, Athens, GA) and insertion of a CIDR (Pfizer Animal Health) on d −9, a PGF2α injection and CIDR removal on d −3, and an injection of GnRH on d 0 for all heifers. Statistical Analysis. For each treatment evaluated, animal was used as the experimental unit because the treatment applied was movement to a grazing situation and was applied to each individual animal. In addition, there was sufficient forage present in the pastures, and all animals were allowed to freely move around each pasture and were allowed to consume ad libitum intake. The effects of adaption to grazing on ADG, number of steps taken, and amount of time standing or lying were analyzed by ANOVA for repeated measures using the MIXED procedures (SAS Institute Inc., Cary, NC) as described by Littell et al. (1998). All covariance structures were modeled in the initial analysis; indicated best-fit covariance structure for BW was compound symmetry, anteindependent for ADG, and heterogeneous compound symmetry for pedometer data and were used for the final analysis. The model included the independent variables of treatment, day, and treatment × day. When a significant (P ≤ 0.05) effect of treatment, day, or treatment × day
was detected, least squares means were separated by the Pdiff option (SAS Institute Inc.).
Exp. 2 Experimental Design. Anguscross beef heifers (n = 301) at 2 locations were developed within location as a single group from weaning until AI on a corn-silage concentrate diet. At time of AI, heifers were randomly assigned to 1 of 2 treatments: (1) moved to pasture (RNG) or (2) moved to pasture and supplemented with 2.2 kg per heifer per day of dried distillers grains plus solubles for 42 d (RNG-SUPP). Forage biomass and nutrient compositions were determined when heifers were moved to pastures (d 0; Table 1). Biomass was determined by clipping useable forage at a height of 2.54 cm within a 0.96m2 loop. Forage samples were weighed and dried, and DM forage was calculated (Table 1). Primary grasses at location 1 were smooth brome (Bromus inermis), quackgrass (Elytrigia repens), and Kentucky bluegrass (Poa pratensis). Primary grasses at location 2 were smooth brome (Bromus inermis), big bluestem (Andropogon gerardi), quackgrass (Elytrigia repens), and Kentucky bluegrass (Poa pratensis). All heifers were synchronized with an injection of GnRH (100 μg i.m. as 2 mL of Cystorelin i.m.; Merial) and insertion of a CIDR device and 7 d later an injection of PGF2α (25 mg i.m. as 5 mL of Lutalyse i.m.; Pfizer Animal Health) at time of CIDR removal. At location 1 (n = 143; 406.9 ± 3.1 kg), estrus detection was done with the aid of EstroTect (Western Point Inc., Apple Valley, MN) estrusdetection aids, and approximately 12 h following the initiation of standing estrus, heifers were inseminated by 1 of 3 technicians to a single sire. Heifers not detected in estrus were inseminated at 72 h after CIDR removal with an injection of GnRH (100 μg i.m.) concurrent with insemination. An equal number of heifers inseminated at 72 h with GnRH were assigned
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Table 1. Nutrient composition and quantity of forage biomass at time of heifer turnout for each location1 Location 1 Item DM, % CP, % TDN, % ADF, % NDF, % Forage DM, kg/ha
Location 2
RNG
RNG-SUPP
RNG
RNG-SUPP
57 15.9 67 30 52.2 2,173
48 13.8 62 34.2 51.4 1,278
55 10.3 63 37 60.9 1,894
40 8.7 60 41.9 65.5 985
At time of AI, heifers were randomly assigned to 1 of 2 treatments: (1) moved to pasture (RNG) or (2) moved to pasture and supplemented with 2.22 kg per heifer per day of dried distillers grains plus solubles (24% CP) for 42 d (RNG-SUPP).
1
to each treatment. At location 2 (n = 158; 432.4 ± 3.2 kg), all animals were inseminated 54 h after CIDR removal by one technician to 1 of 2 sires. An injection of GnRH (100 μg i.m.) was given concurrent with insemination. Following insemination, heifers were immediately placed in their treatment group and remained in treatment groups until pregnancy was determined by transrectal ultrasonography on d 42. Bulls were placed with heifers 14 d following the final AI for the remainder of the breeding season (30 d at location 1 and 60 d at location 2). Artificial-insemination conception rates were determined by transrectal ultrasonography on d 42. Breeding-season pregnancy rates were determined 30 to 50 d after bulls were removed at each location. Statistical Analysis. Given the binary nature of the data, if one animal consumed more than their share of the supplement and another animal consumed less, the benefit to the animal consuming more (i.e., pregnant) would be canceled out by the decreased intake of the other animal (i.e., not pregnant). Thus, each individual animal was used as the experimental unit, and pregnancy data were analyzed using the GLIMMIX procedure (SAS Institute Inc.). The model included treatment, sire, location, BCS at AI, and the treatment × location interaction. When a significant (P ≤ 0.05) effect was detected, least
squares means were separated by the Pdiff option (SAS Institute Inc.).
RESULTS AND DISCUSSION Exp. 1 There was a treatment (P < 0.01), day (P < 0.01), and a treatment × day (P < 0.01) interaction on ADG (Figure 1). Heifers on GRS had decreased (P < 0.01) ADG from d −44 to −35 compared with DLT heifers. There was no difference between treatments in ADG from d −35 to −19 or from d −19 to −3. Following being moved to spring forage, DLT heifers had decreased (P < 0.01) ADG from d −3 to 9 and from d 9 to 30 compared with GRS heifers. In this experiment, naïve (DLT) heifers lost BW compared with heifers that had an adaption period to grazing. This loss in BW was similar to previous reports when heifers were moved to a spring grazing situation after being developed in a drylot from weaning to breeding (Perry et al., 2013). From d −19 to −6, there was an effect of treatment (P < 0.01), day (P < 0.01), and a treatment × day (P = 0.03) interaction on the number of steps taken each day (Figure 2), with GRS heifers taking more (P < 0.05) steps per day than DLT heifers. Following being moved to spring forage, DLT heifers took more (P <
0.05) steps per day on d 0, 1, 2, and 3 compared with GRS heifers (Figure 3). This increase in activity was similar to dairy heifers that did not have prior grazing experience compared with heifers that had previously grazed pastures (Lopes et al., 2013). However, across the entire experiment there was no treatment effect on the amount of time a heifer spent standing or lying per day. Therefore, DLT heifers took more steps in the same amount of time as the GRS heifers, which means more time was spent investigating the new environment and less time was spent grazing by the DLT heifers. The majority of grazing behavior is learned when an animal transitions from maternal care to independence (Provenza and Balph, 1988); this learning results in the development of the motor skills necessary to harvest and ingest forages efficiently (Provenza and Balph, 1987). Furthermore, the willingness to try novel food declined as an animal aged (Provenza and Balph, 1988). Thus livestock usually ingest small amounts of novel food and gradually increase the amount ingested if no adverse effects occur (Chapple and Lynch, 1986; Burritt and Provenza, 1987). When introduced to novel food or environment, livestock may spend more time and energy foraging (Osuji, 1974) but ingest less food (Arnold and Maller, 1977; Hodgson and Jamieson, 1981; Curll and Davidson, 1983). When dairy heifers that had been developed in confinement were moved to pasture, it took 5 d for them to develop a similar grazing pattern as experienced animals (Lopes et al., 2013). Similarly, in this experiment 5 d after being moved to pasture, DLT heifers took a similar number of steps as GRS heifers. However, ADG was decreased for 30 d after being moved to pasture. This decrease is similar to the report of Perry et al. (2013), where inexperienced heifers had decreased ADG compared with experienced heifers for the first 27 d after being moved to grazing.
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Exp. 2
Figure 1. Average daily gain (means ± SE) for heifers in Exp. 1. Heifers on GRS were moved from the drylot to forage on d −44, and DLT heifers were moved from the drylot to forage on d 0. **P < 0.01 within day.
Figure 2. Number of steps taken per day (means ± SE) from d −19 to −6 of treatments in Exp. 1. Heifers on GRS were moved from the drylot to forage on d 0. Heifers on GRS were moved to a new pasture on d −9 and 0. Heifers in DLT were still in the drylot (P < 0.05). Days that GRS heifers were moved to the working facilities for collection of weight data or synchronization were removed from the data analysis (d −14 and −13).
Forage quality within each of the pastures had adequate CP and energy to allow BW gain of animals (Table 1), based on nutrient recommendations (NRC, 2000). Additionally, available forage biomass was not limiting consumption using an average consumption rate of 12 kg per heifer per day for a 454-kg animal unit (Smart et al., 2010). Hence, all groups of animals in Exp. 2 had enough forage available and excess nutrients required for BW gain when moved to grass. However, conception rates to AI were affected by treatment (P = 0.02), with RNG-SUPP heifers having increased pregnancy success compared with RNG heifers (76 ± 7.5% and 61 ± 9.7%, respectively). There was no effect of location (P = 0.64), or treatment by location (P = 0.21), or BCS at AI (P = 0.40) on AI conception rates. Breeding-season pregnancy rates were not different (P = 0.20) between RNG and RNG-SUPP heifers (91 ± 3.4% and 94 ± 2.4%, respectively). Undernourishment due to lack of feed availability or poor-quality feed has been reported to be detrimental to reproductive functions and efficiency (Diskin et al., 2003). In this experiment, animals were not undernourished based on forage nutrient analysis, and based on this analysis animals consuming 2% of BW would gain >0.45 kg/d. However, if animal activity increased (as reported in Exp. 1) and animals did not consume sufficient forage, this situation could cause a short period of undernourishment, possibly affecting AI conception rates. Heifers on RNG-SUPP consumed dried distillers grains plus solubles at an average rate of 2.22 kg per heifer per day, supplying 0.66 kg of CP and 4.8 Mcal of supplemental nutrients. If RNG-SUPP consumed 3.0 kg of forage DM, the animals would have met their nutrient requirement for 0.22 kg/d of BW gain; however, the nutrients of the RNG heifers were acquired from only forage, and they would have had to consume 5.8 kg of DMI/d to meet the same BW-gain goal. A
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ent intake and increased activity as unexperienced heifers took more steps daily compared with adapted heifers. Supplementing heifers when they were moved to a forage grazing situation resulted in improved AI conception rates compared with moving heifers to a pasture without supplementation. Therefore, when heifers are developed in a drylot situation, high AI conception rates are possible, but management decisions need to be considered to avoid allowing heifers to enter a negative energy balance immediately following AI.
IMPLICATIONS Figure 3. Number of steps taken per day (means ± SE) from d 0 to 8 of treatment in Exp. 1. Heifers on GRS were moved from the drylot to forage on d −44. Heifers in DLT were moved from the drylot to forage on d 0. *P < 0.05.
decrease in feed intake from 120% of maintenance to 40% of maintenance resulted in a BW loss of 1.83 kg/d for a 2-wk period, and the majority of heifers stopped having normal estrous cycles (Mackey et al., 1999). Heifers fed only 85% maintenance requirements of energy and protein had reduced embryo development on d 3 and 8 after insemination compared with heifers fed 100% maintenance (Hill et al., 1970). Pregnancy establishment is dependent on oviductal and uterine secretions (Spencer and Bazer, 2004), including nutritional factors that are required for embryo growth and survival (Gao et al., 2009; Block et al., 2011). This decrease in energy intake could have a direct effect on changing the uterine environment by changing components of uterine secretions or an indirect effect by influencing the circulating concentrations of progesterone that regulate the uterine environment (Foxcroft, 1997). Hill et al. (1970) observed an immediate reduction in corpus luteum size and circulating concentrations of progesterone in heifers exposed to nutrient restriction. However, neither Spitzer et al. (1978) nor Rhodes et al. (1995) reported a difference in circulating concentrations of proges-
terone in heifers following nutrient restriction. A decrease in nutrient intake, as determined by ADG, when drylot-developed heifers were moved to a grazing situation immediately following insemination resulted in decreased AI conception rates (Perry et al., 2013). In this experiment, supplementing drylot-developed heifers for 42 d following insemination resulted in improved AI conception rates compared with heifers that were not supplemented. It was not determined what duration of supplementation was needed to increase pregnancy success. The duration of 42 d was used to keep heifers on a positive level of nutrition until pregnancy determination. In addition, by this point of pregnancy the fetus is completely attached to the uterus (Fléchon and Renard, 1978) and incidence of embryonic mortality is reduced. Research from our laboratory has indicated that after 27 d of grazing, ADG is similar between heifers developed on range and heifers developed in a drylot (Perry et al., 2013). In summary, following being moved to spring forage, drylot-developed heifers had decreased ADG compared with heifers that had prior grazing experience. This decrease in ADG is likely because of decreased nutri-
Achieving optimal AI conception rates with heifers developed in drylots requires management that avoids negative BW loss immediately following AI. Management options include (1) adaption to grazing before AI, (2) supplementation for animals while on pasture for approximately 30 d, or (3) retention of heifers in drylot until after AI.
ACKNOWLEDGMENTS This research was supported by the South Dakota Agricultural Experiment Station and the South Dakota Corn Utilization Council. Mention of a proprietary product does not constitute a guarantee or warranty of the product by South Dakota Agricultural Experiment Station or the authors and does not imply its approval to the exclusion of other products that may also be suitable. The authors gratefully acknowledge Pfizer Animal Health for their contribution of CIDR and Lutalyse and S. Fields, J. Krantz, J. Nelson, and C. Wright at South Dakota State University for their technical assistance.
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