ANSC 4380- Beef Cattle #2 Questions With 100% Correct!!

Cross Breeding - the mating of individuals with different breed make-up -widely used in commercial beef production systems -improvements in production efficiency can be dramatic -does not eliminate the need for purebreds Heterosis - the average superiority of a crossbred individual over the average of breeds involved n the cross -arises from combining genes from different breeds so inferior recessive genes are concealed -offspring may be better than either paternal breed or better than average of the two Types of Heterosis: - -individual heterosis -maternal heterosis -paternal heterosis Individual Heterosis - (Calf) the advantage of the crossbred individual relative to purebred individual Maternal Heterosis - (Dam) advantage of the crossbred mother over the average of the purebred mothers Paternal Heterosis - (Sire) advantage of the crossbred male over the average of purebred males (testis characteristics & conception rate) Levels of Heterosis - 3 major categories: -reproduction (high levels) -growth traits (medium levels)-carcass traits (high levels): not much benefit Crossbreeding Systems - -terminal systems: feed lot, growth, beef -rotational systems: produce replacement heifers (maternal) -combination of the two: large producers Terminal Systems - specific breed of sire is mated to a specific breed of dam -2 breed: 100% individual heterosis -3 breed: 100% maternal heterosis -4 breed: 100% paternal heterosis breeds complementary is the main advantage of terminal systems since male & female breeds can be chosen for specific roles Male & female roles in terminal systems: - males: should excel in growth & carcass merit females: should excel in reproductive performance & mothering ability Terminal Cross System - -easy to use -only one breed of bull is used, so one breeding pasture -replacements must be purchased: can introduce disease, no control over selection practices Rotational Systems - -generate their own replacement females -each cycle uses a different breed of bull -females are kept from each cycle -always some element of back crossing (heterosis is lost) Advantages of Rotational Systems: - -replacements are produced -less chance for introduction of disease -producer can exercise selectionDisadvantages of Rotational Systems: - -breed complementarity is reduced/lost (each breed needs to be somewhat terminal & maternal) -multiple bulls (breeds) & pasture needed Breeds in Rotational Systems - any # of breeds can be used; the more breeds the more heterosis retained in the herd -2 breeds: 67% -3 breeds: 86% -4 breeds: 93% Combination Systems - large producers are capable of using both rotational & terminal -replacements in rotational -market calves in terminal Advantages of Combination Systems - -produces replacements with outstanding maternal performance -provides calves with a good growth & carcass merit Disadvantages of Combination Systems - -could be difficult to maintain -requires a large herd for efficient utilization -requires segmentation of the herd into smaller components Breed Choice - -vitally important -large differences among breeds for many traits of economic importance -inferior breeding stock can canal out heterosis -careful consideration must be made in designing a breeding system Composites - -a hybrid with at least two or more breeds in its background -bred to their own kind-return a level of heterosis normally associated with traditional crossbreeding systems Breeding Soundness Exam - -should be performed at least 60 days prior to each breeding season (not "one & done") -3 combinations to a BSE: physical exam, exams of reproductive tract, semen evaluation (monthly, morphology concentration, color) Libido - willingness & eagerness to breed females -general views of bull libido: 1) fairly large genetic component 2) bulls naturally polygamous 3) pre-mating stimulation increases sexual response 4) competition increases sexual response Mating Ability - physical ability & competence to breed females Bull Reproduction - -seminal quality in young bulls has been shown to improve for up to 16 weeks after puberty (puberty ≠ full fertility) -herd sires should have at least 32 cm scrotal circumference when put with cows (2-year old min 34cm SC) -there is an increase in semen quality as SC increases, up to -38 cm -scrotal shape is also important in bull fertility Weaned Bull Calves - -common mistake is failure to provide adequate nutrition -often turned out and allowed to "rough it" until breeding season -1st step to providing adequate nutrition is to determine desired growth amount -young bulls have 160 days to go from weaning age to yearling age (need to gain 2.5 lb/d or more) Rations for weaned bull calves - as weight increases, feed consumption needs to increase; may need protein supplement due to quality of hayshould include: -concentrated fed at about a minimum of 2% of BW -alfalfa hay or grass hay free choice -for a 600 lb bull, 12 lb concentrate & 6 lb hay -goal = rapid growth without excessive fattening Grain feeding bull calves - -should begin gradually & bring bulls up to desired intake over a period of at least 2 weeks -small grains pasture such as ryegrass, wheat, & oats can be used to produce similar rates of gain (provide appropriate mineral mixes, critical needs of Ca & Mg) Gain-tested Bulls - -reduce fleshiness of the bull prior to the breeding season -feed them a ration similar to what they have been on at 60-70% of previous intake then reduce by about 10% per week until desired level achieved. --replace grain with hay, add protein in needed -dramatic nutritional changes can have adverse effects on fertility Yearling Bulls - -should be well grown but not too fat -should reach puberty 3-4 mo. prior to breedings -age at puberty depends on size/weight & breed -semen production is dependent on overall growth, tests development & other reproductive organs -size of tests & semen volume are positively correlated -fed diets similar to weaned bull calves -left with cows for 60 days or less Bull to Cow Ratios - 3 goals of breeding season: 1) get as many cows settled early in season as possible 2) get them bred to bulls with the highest possible genetic worth 3) achieve both as economically as possible by getting cows bred with fewest # of bulls (1 to 25 bull to cow ratio is ideal; no ratio is optimal for all ranchers)How does the # of bulls affect the bull to cow ratio? - -distribution of breeding females -terrain -water availability -carrying capacity & feed intensity -pasture size Bull variation is caused by: - -age -condition -mating ability -libido -fertility -sperm reserve -social behavior -injury Bull overlap in bull to cow ratios: - not desirable: -does not enhance pregnancy rates -increases risk of bull injury -increases pressure/stress from social dominance -expensive: more bull than needed eliminated by: -divided hers into separate pastures -using pastures with natural barrier -riders to keep bull separated