title: Development of a Lifetime Merit-based selection index for US dairy grazing systems.
abstract: Pasture-based dairy producers in the United States face costs, revenue streams, and management challenges that may differ from those associated with confinement dairy production systems. Three Grazing Merit indices (GM$1, GM$2, and GM$3), parallel to the US Lifetime Net Merit (NM$) index, were constructed using economic values appropriate for grazing production in the United States. Milk prices based on averages from the previous 5 yr were used for GM$1, whereas GM$2 and GM$3 used milk prices found in NM$. Cull prices and interest rates from NM$ were used in GM$3 but were updated for GM$1 and GM$2. All other inputs remained constant among GM$1, GM$2, and GM$3. Economic costs and revenues were obtained from surveys, recent literature, and farm financial record summaries. Derived weights for GM$ were then multiplied by the predicted transmitting abilities of 584 active artificial insemination Holstein bulls to compare with NM$. Spearman rank correlations for NM$ were 0.93 with GM$1, 0.98 with GM$2, and 0.98 with GM$3. Traits (and their percentages of weight) comprising GM$1, GM$2, and GM$3, respectively, included milk volume (24, 0, 0%), Fat yield (16, 21, 21%), protein yield (4, 17, 17%), productive life (7, 8, 7%), somatic cell count (-8, -9, -9%), feet and legs composite (4, 4, 4%), body size composite (-3, -4, -4%), udder composite (7, 8, 8%), daughter pregnancy rate (18, 20, 20%), calving ability (3, 3, 3%), and dairy form (6, 6, 6%). These weights compared with NM$ weights of 0, 19, 16, 22, 10, 4, 6, 7, 11, 5, and 0% for the same traits, respectively. Dairy form was added to GM$ to offset the decrease in strength associated with selection to reduce stature through selection against body size. Emphasis on productive life decreased in GM$ because grazing cattle are estimated to remain in the herd considerably longer, diminishing the marginal value of productive life. Although NM$ provides guidance for grazing dairy producers, a GM$ index based upon appropriate costs and revenues allows for selection of cows and bulls for more optimal genetic progress.
authors.affiliation: Department of Animal Sciences, Purdue University, West Lafayette, IN 47907-2042.
authors.forename: K D
authors.initials: KD
authors.lastname: Gay
authors.affiliation: Department of Agricultural Economics, Purdue University, West Lafayette, IN 47907-2042.
authors.forename: N J O
authors.initials: NJ
authors.lastname: Widmar
authors.affiliation: Department of Animal Sciences, Purdue University, West Lafayette, IN 47907-2042.
authors.forename: T D
authors.initials: TD
authors.lastname: Nennich
authors.affiliation: Department of Animal Sciences, Purdue University, West Lafayette, IN 47907-2042.
authors.forename: A P
authors.initials: AP
authors.lastname: Schinckel
authors.affiliation: Animal Improvement Programs Laboratory, Agricultural Research Service, USDA, Beltsville, MD 20705-2350.
authors.forename: J B
authors.initials: JB
authors.lastname: Cole
authors.affiliation: Department of Animal Sciences, Purdue University, West Lafayette, IN 47907-2042. Electronic address: mschutz@purdue.edu.
authors.forename: M M
authors.initials: MM
authors.lastname: Schutz
mesh_terms: D000818:Animals; D001947:Breeding; D002417:Cattle / Q000235:genetics / Q000502:physiology*; D003612:Dairying / Q000191:economics / Q000379:methods*; D005260:Female; D008297:Male; D018803:Models, Economic; D011247:Pregnancy; D014481:United States
keywords: economic value; genetic; grazing; selection index