Jackson County Heifer Development Project Summary

The heifer development project was a five year project conducted on the site of the former Jackson County Farm north of Andrew, Iowa, for four years and on an area producer’s farm for the fifth year. Heifers arrived around December 1 each year and the average number of heifers each year was 43 with a low of 37 and high of 47. After a 30+ day warm-up period the heifers were put on a 112-day test from early January to late April. They were fed a shelled corn and legume-grass hay ration consisting of between 13% and 14% crude protein and a range of .44 to .58 megacal/pound of NEg over the five years. During the 112-day test heifers gained 1.86, 1.78, 1.5, 1.63 and 2.2 pounds per day, respectively, for years 1992 through 1996. The actual average breeding weight was less than the target weight in three years by 5, 12 and 22 pounds and exceeded the target weight in two year by 17 and 28 pounds. Estrus synchronization used a combination of MGA feeding and Lutalyse injection. Heifers were heat detected and bred 12 hours later for a three-day period. On the fourth day, all heifers not bred were mass inseminated. Heifers then ran with the cleanup bull for 58 days. The average synchronization response rate during the project was 79%. The overall pregnancy rates based on September pregnancy averaged 92%. The five year average total cost per head for heifer development was $286.18 or about $.85 per day. Feed and pasture costs averaged 61% of the total costs.

Jackson County Heifer Development Project Update

The heifer development project took place the past four years on the site of the former Jackson County Farm north of Andrew, Iowa. Heifers arrived around December 1 with 38 heifers delivered for 1992, 44 for 1993, 46 for 1994, and 47 for 1995. After a 30+ day warm-up period, the heifers were put on a 112-day test from early January to late April. They were fed a shelled corn and legume-grass hay ration consisting of between 13% and 14% crude protein and .48, .58, .44, and .54 megacal/pound of NEg respectively for the years 1992 - 1995. During the 112-day test heifers gained 1.86, 1.78, 1.5, and 1.63 pounds per day respectively for years 1992 through 1995. The 1995 heifers averaged 853 pounds at breeding (22 pounds under target weight). This compares with previous years in which the breeding weight was less than target weight in two years by 5 and 12 pounds and exceeded the target weight in one year by 17 pounds. Estrus synchronization used a combination of MGA feeding and Lutalyse injection. Heifers were heatdetected and bred 12 hours later for a three-day period. On the fourth day, all heifers not bred were mass inseminated. Heifers then ran with the cleanup bull for 58 days. The synchronization response rate in 1995 was 83%, which compares with the three year previous average of 77%. The overall pregnancy rates based on September pregnancy exams were 94.6% in 1992, 93% in 1993, 91% in 1994, and 91.5% in 1995. Development costs for the 326 days in 1995 totaled $269.14 per heifer. This compares with the average of $286. 92 for the three previous years. The four-year average total cost per head for heifer development was $282.48, or about $.84 per day. Feed and pasture costs represented 58% of the total costs, or $.49 per day.

The Use of a Vaginal Conductivity Probe to Influence Calf Sex Ratio via Altered Insemination Time

One hundred eighty-nine mixed breed beef heifers from 13 consignors enrolled in the MACEP heifer development project were utilized in this study. Heifers were synchronized by feeding 0.5 mg melengestrol acetate (MGA) per head per day for 14 days followed by an injection of prostaglandin F2a (PGF2a; 25 mg Lutalyse®) 17 days after the last MGA feeding. Each heifer was fitted with a Heatwatch® transmitter on the morning of PGF2a administration to facilitate detection of estrus. Vaginal conductivity measurements were taken using an Ovatec® probe every 12 hours for 96 hours beginning at the time of PGF2a injection. Heifers randomly assigned to produce a female calf were inseminated near the onset of estrus (as indicated by probe values of £ 55 on the decline). Heifers randomly assigned to produce a male calf were inseminated approximately 24 hours after the onset of estrus (as indicated by probe values of ³ 60 on the incline). All heifers not inseminated by 96 hours after PGF2a were mass inseminated in an attempt to impregnate as many heifers as possible. Heifers that were diagnosed as pregnant as a result of the artificial insemination were subjected to ultrasonography for fetal sex determination. Only 70 of the 189 heifers (37.0%) exhibited estrus according to Heatwatch® and incidence of estrus was influenced by heifer average daily gain, reproductive tract score, and disposition score. Heifers receiving a disposition score of 3 (78.7) had a higher (P<.05) probe reading at AI than those receiving a disposition score of 1 or 2 (70.8 and 72.5, respectively). Heifers with probe readings at insemination of 80 - 84 and > 84 had lower (P<.05) pregnancy rates to AI (13.6 and 0.0%, respectively) than heifers with probe readings in the ranges of < 60, 60 - 64, 65 - 69, 70 - 74, and 75 - 79 (35.7, 40.9, 31.4, 35.3, and 26.9% respectively). Heifers that were bred when probe values were increasing had a lower (P<.05) percentage of male fetuses (34.4%) than those bred during a period of decreasing probe values (69.2% male fetuses). These results demonstrate that a vaginal conductivity probe may be a useful tool to determine an insemination time that could potentially alter calf sex ratio.