Final Report for LNC07-278

Project Type: Research and Education
Funds awarded in 2007: $149,026.00
Projected End Date: 12/31/2010
Region: North Central
State: South Dakota
Project Coordinator:
Dr. George Perry
South Dakota State University
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Project Information

Summary:

The cost of developing replacement heifers has a tremendous impact on the profitability of cow-calf operations, and the economic value of reproduction for commercial beef producers has been reported to be five times greater than calf growth. Therefore, methods of heifer development that decrease costs but maintain high reproductive performance can have a tremendous impact on profitability. The first objective of this project compared two methods of heifer development (wintered in a feedlot or on grass) and three diets initiating after artificial insemination (maintain weight, gain weight on a diet high in metabolizable protein or low in metabolizable protein). Although there were no differences between heifer development methods, diet impacted both uterine pH and blood urea nitrogen concentrations. Both uterine pH and blood urea nitrogen can influence pregnancy success, and therefore have a tremendous impact on the economics of heifer development and ranch profitability. The second objective determined the influence of post-AI change in nutrition on pregnancy success and embryonic loss. The percentage of heifers that had reached puberty prior to the start of the breeding season tended to be more in the feedlot developed heifers compared to the range developed heifers. However, heifers developed on range tended to have greater pregnancy success compared to heifers developed in the feedlot. The third objective was to demonstrate the benefit of forage-based heifer development compared to traditional feedlot developed heifers. For this objective we worked with 7 producers and over 1300 heifers. Weight change data from AI to pregnancy determination was collected on over 800 heifers, and pregnancy success was decreased when heifers lost weight from AI to pregnancy determination (30 to 65 days). However, when heifers were developed on grass, there was no effect on pregnancy success weather they were returned to grass and supplemented or not or even kept in the feed lot.

Introduction:

The cost of developing replacement heifers has a tremendous impact on the profitability of cow-calf operations. Cow-calf production systems that rely heavily on harvested and purchased feeds have less potential to be profitable (Adams et al., 1994), and an important part of any production system is reproductive performance and costs associated with developing heifers. The economic value of reproduction for commercial beef producers was reported to be five times greater than calf growth (Trenkle and Willham, 1977).
Heifer development throughout the North Central Region of the U.S. usually involves placing heifers into a confined feeding situation from weaning until the following breeding season. Development of heifers in a confined environment can create several management problems; the greatest of which are the labor and cost involved with daily feeding. Developing heifers on range is not a common practice in the North Central Region of the U.S. due to the perception that adequate reproduction cannot be maintained in such a system. It is hypothesized that a range supplementation management system could be used to develop replacement heifer calves.
Following insemination, heifers are usually turned to grass and are often not supplemented. Spring grass can vary tremendously in nutrient content, and producers often ask if the change in diet following insemination will reduce pregnancy rates. It is possible that energy and protein requirements may be undersupplied or oversupplied and therefore increases embryonic mortality. Supplementation following insemination to balance nutrients may therefore increase pregnancy rates.
Development and utilization of forage-based heifer development and post-insemination supplementation will reduce the number of animals fed in confinement situations, decrease cost and improve the reproductive efficiency of heifer development. This will allow ranchers to be more profitable by decreasing the labor involved with heifer development and allowing them more time to devote to other obligations.

Project Objectives:

Overall Objective: Evaluate the benefits of forage-based heifer development and determine appropriate post-insemination supplementation to maximize heifer performance.

Objective 1: To determine the influence of post-AI change in nutrition on uterine environment and circulating concentrations of plasma urea nitrogen.

Objective 2: To determine the influence of post-AI change in nutrition on pregnancy success and embryonic loss.

Objective 3: To demonstrate the benefit of forage-based heifer development compared to traditional feedlot developed heifers.

Cooperators

Click linked name(s) to expand
  • Jack Davis
  • Patricia Johnson
  • Jim Krantz
  • Julie Walker
  • Cody Wright

Research

Materials and methods:

Specific Aim 1: To determine the influence of post-AI change in nutrition on uterine environment and circulating concentrations of plasma urea nitrogen.

Experimental Procedures.
Heifers were developed under conventional feedlot development strategies or under a forage-based development strategy. At approximately 15 months of age, heifers were allotted to one of three treatments [1: maintain weight (MAIN; 6.4 kg hay and 0.01 kg urea/hd) or to gain weight on a diet high (HMP; 6.2 kg hay, 2.9 kg DDGS and 0.03 kg urea/hd)] or low (LMP; 8.0 kg hay and 0.8 kg DDGS/hd) in metabolizable protein.. All heifers were synchronized utilizing the Select Synch plus Controlled Internal Drug Releasing devise (CIDR) protocol [an injection of GnRH (100 ?g, i.m.) on d 0 and a CIDR placed into the vagina, and on d 7 an injection of PGF2? (25 mg i.m.) and the CIDR removed]. Animals were moved to their respective treatment when they are detected in standing estrus. Blood samples and uterine pH were collected at estrus (day 0) and on day 7 and 11 to determine changes in blood urea nitrogen and uterine environment.

Specific Aim 2: To determine the influence of post-AI change in nutrition on pregnancy success and embryonic loss.

Experimental Procedures.
Weaned heifers were developed from weaning to breeding either in a feedlot (n=52; LOT) or on grass (n=53; GRASS). Immediately following fixed-time AI all heifers were moved to the same pasture. Blood samples were collected from all heifers on d -23, -9, the day of AI (d 0), and d 11. Pregnancy success was determined 42 d following AI.

Specific Aim 3: To demonstrate the benefit of forage-based heifer development compared to traditional feedlot developed heifers.

Experimental Procedures.
Seven cooperators developed between 100 and 200 heifers each on forage or in a drylot and/or supplemented post-AI. Records were kept to determine changes in heifer performance and reproductive performance.

Research results and discussion:

Objective 1 has been completed and data has been submitted to the Midwest section of the American Society of Animal Science.
Results: Weaned heifers were developed to gain 0.454 kg/d for 6 mo either in the feedlot (LOT) or on grass (GRASS). All heifers were synchronized with a CIDR protocol and AI was performed following detection in estrus. Following AI all heifers were moved to a feedlot and each development group, LOT and GRASS, was divided into 3 groups. The groups were fed to maintain weight (MAIN; 6.4 kg hay and 0.01 kg urea/hd) or to gain weight on a diet high (HMP; 6.2 kg hay, 2.9 kg DDGS and 0.03 kg urea/hd)] or low (LMP; 8.0 kg hay and 0.8 kg DDGS/hd) in metabolizable protein. Uterine pH and blood samples were collected from a subset of each group (n=3 LOT and 3 GRASS per post-AI group) on d 0, 7, and 11 after estrus. There was no difference (P>0.20) in Body Weight between MAIN, HMP, or LMP heifers on the day of AI (311±3.6 kg), but heifers in the HMP and LMP group weighed more (P?0.01) than heifers in the MAIN group on d 11 (344±5.5, 338±5.5 kg, and 315±7; respectively). Uterine pH did not differ (P>0.14) between LOT and GRASS heifers; however, uterine pH decreased (P?0.01) from d 7 to d 11 and was lower (P=0.03) among heifers fed HMP compared to heifers fed LMP or MAIN. There was no difference (P>0.18) between lot and grass developed heifers for blood urea nitrogen (BUN); however, there was a post-AI treatment by time interaction (P?0.01). LOT and GRASS heifers had similar (P>0.14) BUN concentrations on d 0. BUN concentrations in LMP heifers did not change from d 0 to d 7 or 11. BUN increased from d 0 to d 7 and 11 in both MAIN (P?0.04) and HMP (P?0.01). In summary, method of heifer development (LOT or GRASS) did not influence uterine pH or BUN when heifers were fed in a feedlot following AI; however, post-AI diet had an impact on both uterine pH and BUN.

Objective 2: has been completed and data is being utilized for field trial that will be completed this summer.
Results: Weaned heifers were developed from weaning to breeding either in a feedlot (n=52; LOT) or on grass (n=53; GRASS). Immediately following fixed-time AI all heifers were moved to the same pasture. Blood samples were collected from all heifers on d -23, -9, the day of AI (d 0), and d 11. Pregnancy success was determined 42 d following AI. There tended (P=0.10) to be more LOT heifers cycling prior to the breeding season (94% vs 84%), but GRASS heifers tended (P=0.20) to have greater pregnancy success (57% vs. 44%). There were effects of development (P?0.01), time (P?0.01), and development by time (P=0.02) on glucose concentrations. Glucose concentrations decreased from d 0 to d 11 in both groups. Glucose was greater (P?0.01) in GRASS compared to LOT heifers (P?0.01; 87.3 ± 1.24 and 80.2 ± 1.25 mg/dL) on d 0 but similar (P=0.43; 76.29 ± 1.24 and 74.9 ± 1.24 mg/dL) on d 11. Pregnant heifers had greater glucose than open heifers on d 11 (P= 0.04; 77.4 ± 1.24 and 73.8 ± 1.24 mg/dL) but not on d 0 (P=0.88). Concentrations of PUN were influenced by development (P?0.01) and time (?0.01). Concentrations increased from d 0 to 11, and were greater in GRASS (12.9 ± 0.22 and 15.1 ± 0.22 mg/dL) compared to LOT (11.8 ± 0.22 and 13.6 ± 0.22 mg/dL) heifers. There tended (P=0.07) to be a development by pregnancy interaction with similar (P=0.54) PUN concentrations between LOT pregnant and open heifers, but greater (P=0.04) concentrations in GRASS open compared to GRASS pregnant heifers. Method of heifer development (LOT or GRASS) influenced both glucose and PUN concentrations with GRASS heifer having greater glucose and PUN concentrations compared to LOT heifers, and pregnant heifers tended to have greater glucose than open heifers.

Objective 3: To demonstrate the benefit of forage-based heifer development compared to traditional feedlot developed heifers.
Results: In cooperation with 7 producers, beef heifers (n = 1338) have been managed to look at weight change after AI on pregnancy success. At two locations (n = 144 and 164 at location 1 and 2, respectively) were developed in a feedlot from weaning to breeding. At time of insemination heifers were randomly allotted to one of two treatments: 1) heifers were moved from the feedlot to graze spring forage, or 2) heifers were moved to graze spring forage and supplemented with DDGS (5 lbs/hd/day) for 42 days. Pregnancy success was determined 42 days after AI. At location 1, there was no difference between treatments in weight change from AI to pregnancy determination (17 ± 3.9 and 15 ± 3.7 lbs for heifers not supplemented and supplemented; respectively). Pregnancy rates did not differ between treatments (P = 0.54) at location 1 [34 % (24/70) and 39 % (29/74) for heifers not supplemented and supplemented; respectively]. However, at location 2, heifers that were grazing spring forage alone lost ± 4 lbs, but heifers that were grazing spring forage and were supplemented gained 45 ± 3 lbs from AI to pregnancy determination (P?0.01). At location 2, pregnancy success was different between treatments (P = 0.05). Heifers that were not supplemented after AI had decreased pregnancy success (26%) compared to heifers that were supplemented (40%). Therefore, when heifers were developed in a feedlot, pregnancy success tended to be influenced by weight gain after moving heifers to grass. At two locations we determined the influence of moving feedlot developed heifers to grass before time of AI on pregnancy success. At location 3, 333 heifers were developed on grass from weaning to breeding. All heifers were brought into a feedlot and synchronized with a 7 day CIDR protocol. At time of insemination heifers were randomly allotted to one of three treatments: 1) heifers were moved to graze spring forage, 2) heifers were moved to graze spring forage plus supplemented with DDGS (5 lbs/hd/day) for 42 days, or 3) heifers were returned to the feed lot for 42 days. Pregnancy success was determined 42 days after AI. Body condition increased (P < 0.01) from the day synchronization began (day -7; 5.4 ± 0.05) to day 42 in both the heifers that were supplemented on pasture and the heifers that were kept in the feed lot (5.9 ± 0.04 and 5.8 ± 0.04, respectively). Body condition did not change from day -7 to day 42 among the heifers that were on grass alone (5.4 ± 0.05 and 5.4 ± 0.04 for day -7 and day 45, respectively; Table 3). Pregnancy success did not differ between treatments [59% (65/111), 57% (63/111), and 56% (62/111) for heifers on grass alone, heifers on grass plus supplemented, and heifers in the feed lot, respectively). At location 4 and 5, 50 and 191 heifers, respectively, were equally divided into 2 treatments: 1) moved to grass 30 days prior to breeding and 2) left in the feedlot until breeding. At location 4, from breeding to pregnancy determination (day 35) heifers moved to grass early gained 17 lbs but heifers left in the feedlot only gained 0.6 lbs (P = 0.07). Final AI pregnancy success was 57% (12/21) for grass heifers and 46% (11/24) for lot heifers. At location 5, from breeding to pregnancy determination (day 70) heifers moved to grass early gained 105 lbs but heifers left in the feedlot only gained 2.8 lbs (P < 0.01). Final AI pregnancy success following detection in standing estrus was 63% (52/82) and 58% (46/80) for heifers moved to grass and left in the lot, respectively. Combined pregnancy rates were 62% and 55% for heifers moved to grass and left in the lot, respectively (P = 0.28). At location 6, 296 heifers were developed in the feedlot from weaning to breeding and remained in the feedlot after insemination until pregnancy determination. At location 7, 160 heifers were developed in the feedlot from weaning until breeding and were all moved to grass after insemination. Across all of these studies weight change from AI to pregnancy determination seemed to have the greatest impact on pregnancy success. Weight change data has been collected on over 800 heifers, and pregnancy success has been decreased when heifers lost weight from AI to pregnancy determination (30 to 65 days). However, when heifers were developed on grass, there was no effect on pregnancy success weather they were returned to grass and supplemented or not or even kept in the feed lot.

Research conclusions:

Recent data from our laboratory has indicated that heifers can be developed on native range, and reproductive performance can be maintained. Therefore this proposal evaluated the reproductive performance differences between heifers developed in a conventional system and ones developed on forage. Results from the first objective demonstrated that method of heifer development had no impact on uterine pH or blood urea nitrogen, but the diet that heifers were moved to following AI did impact both uterine pH and blood urea nitrogen. Therefore, method of heifer development during the winter should be decided by cost of development and how heifers will be managed after insemination. Results from objective 2 demonstrated that heifers developed in a feedlot may be more likely to have reached puberty, but when moved to grass immediately after insemination conceptions rates tended to be decreased compared to heifers developed on range over the winter. Objective 3, demonstrated that pregnancy success was decreased when heifers lost weight from AI to pregnancy determination (30 to 65 days). However, when heifers were developed on grass, there was no effect on pregnancy success whether they were returned to grass and supplemented or not or even kept in the feed lot.

Economic Analysis

The daily cost for feed to develop heifers on range was less than the cost to develop heifers in a conventional feed lot situation, but using a commercially available supplement could increase the daily cost for feed. Therefore, cost can vary greatly depending on the cost of feed ingredients, but these costs only include costs for feed, and do not account for any costs for yardage, equipment, or facilities in the feed lot situation. In addition, a charge for the forage used by the range-developed heifers, which account for around half of the cost of development, needs to be estimated. Therefore, the forage development and supplementation can then be utilized in the development of replacement heifers. This method can decrease total production cost, however, the economic value of forage or feedlot developing heifers greatly depends on the value of hay, forage, and supplement.

Farmer Adoption

The goal of this research was to determine if reproductive efficiency could be maintained with alternative heifer development methods, and to determine if it was practical for producers in the Northern Great Plains to utilize these methods. A direct impact of this proposal has been that every producer that participated in the studies changed their method of heifer development to help eliminate nutritional changes following insemination.

Participation Summary

Educational & Outreach Activities

Participation Summary

Education/outreach description:

Data from this proposal has been shared with over 1000 producers at state, regional, and national producer meetings and field days. In addition, this data has contributed to the growing scientific knowledge base on heifer development as it will be included in an invited review paper on puberty and pregnancy success in beef heifers.

Project Outcomes

Recommendations:

Areas needing additional study

Understanding how heifer development can impact reproductive efficiency can have a tremendous impact on the profitability of cow/calf producers in the North Central Region of the United States. However, an area that has not been completely evaluated is how heifer development can impact the longevity of the heifer. Recent data has indicated that it requires 6 year of producing a calf annually for an animal to truly become profitable (capture cost of development and annual maintenance fees). Therefore further evaluation of how heifer development and reproductive efficiency impacts longevity of animals in the herd could have tremendous impact on the sustainability of cattle operations in the North Central Region of the United States.

Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.