Effect of Reduced Gain Prior to Breeding Replacement Heifers
-Preliminary Observations -
|Reducing pre breeding gain to 1 lb. per day significantly
reduced the artificial inseminated (AI) conception rate, but did not significantly affect
overall heifer reproduction. Reducing the rate of gain pre-breeding is not recommended
based on preliminary observations.
|The management of feed costs and gain is critical in any
heifer development program. The goal of developing heifers is to attain maximum conception
rates at the lowest cost possible. The Dickinson Research Extension Center has been
involved in heifer development for four years, and each year has presented the management
team challenging but interesting scenarios. In the spring of 1995, a set of heifers gained
more than projected and were destined to reach breeding weight earlier than expected. The
management team needed to decide to either let the heifers continue to gain and not risk a
set back in reproductive performance or decrease the heifers gain, to lower the cost
of development and risk negatively impacting reproduction. The purpose of this trial was
to determine if decreasing the rate of gain prior to breeding negatively impacted heifer
Materials and Methods
|North Dakota Beef Cattle Improvement Association members
utilizing the CHAPS production testing program were invited to enter raised heifers born
between February and May into the development project conducted in 1995-1996. Consigned
heifers were delivered in November to the Dickinson Research Extension Center-Manning
Ranch Unit. Heifers were managed as described by Ringwall, et al "Production and
Associated Costs of Heifer Development" in the 1998 Dickinson Research Extension
Center Annual Report.
Heifers were given an adaption period in which a receiving ration was fed and health was closely monitored. Once on feed, heifers were weighed on test, body condition scored, frame scored, disposition scored, and allocated to feeding groups based on weight and target gain. Target gain was determined by calculating the gain needed to achieve 70% of a frame score projected mature weight at the start of breeding. Mature weight was projected by the following formula: mature weight = (frame score*75) + 800. Heifers were maintained in these groups, and averaged of 2.0 lbs. per day from January 29 to March 12.
Heifers were reevaluated on March 12 and were randomly allocated to four pens. One of two treatments was randomly assigned to each pen. NRC guidelines and actual feed analysis were used to formulate a total mixed ration designed to meet the desired level of gain for each treatment. Heifers on treatment one were targeted to gain 1.5 pounds per day with treatment two targeted to gain 1.0 pound per day. These high roughage rations consisted of corn silage, oatlage, alfalfa hay, oat hay, and were supplemented with white salt, dicalcium phosphate, and a commercially prepare mineral-vitamin premix that included the ionophore BovatecTM.
Heifers were estrus synchronized with SYNCRO-MATE-BTM to facilitate a single AI service followed by a 45-day natural service cleanup. Estrus activity was monitored and breeding heat detected with the use of KMARTM patches. An overall pregnancy rate and AI conception rate were calculated. Reproductive data was analyzed with Chi-Square procedures through SAS.
Results and Discussion
|The results are presented in Table 1. These heifers were reevaluated on March 12 and the management team concluded that the heifers were gaining more weight than desired. The decision was made to reduce the heifers to two different levels of gain and monitor reproductive performance. Both sets of heifers were gaining at 2.0 lbs. per day and half the heifers were reduced to 1.5 lbs. per day and the other half were reduced to 1 lb. per day. The condition scores were similar for each treatment group with overall body condition increasing slightly over the test period. Reducing pre-breeding gain to 1 lb. per day significantly reduced the AI conception rate, but did not significantly affect overall heifer reproduction. The same negative effect on AI conception was noted regardless if the heifer was gaining less than 2 lbs. per day, or 2 lbs. per day or more, prior to reduced gain treatments started on March 12 (table 2).|
Table 1. Growth and reproductive performance of heifers with reduced gain prior to breeding.
1.5 lbs./day gain
1 lb./day gain
|Number of heifers||23||25|
|Percent estimated mature weight at breeding||67||65|
|Average daily gain|
|January 29 to March 12||2.0||2.0|
|March 12 to May 2||1.5||1.0|
|AI conception percent1||78||33|
|Percent expressing estrous||100||96|
|Overall pregnancy percent||91||84|
1AI conception percent was significantly different (P<.05).
Table 2. Effect of average daily gain before the reduced gain treatments on reproductive performance.
1.5 lbs./day gain
1 lb./day gain
|ADG less than 2 pounds|
|AI conception percent||73||27|
|Percentage expressing estrous||100||100|
|Overall pregnancy percent||91||87|
|ADG 2 pounds or greater|
|AI conception percent||83||44|
|Percent expressing estrous||100||90|
|Overall pregnancy percent||92||80|