The Virginia Tech crossbreeding program began in the fall of 2002 by mating Holstein and Jersey foundation females to Holstein and Jersey bulls to create HH, HJ, JH, and JJ breed groups (sire breed listed first). Collection of daily dry matter intakes (DMI) began in the fall of 2005 and continued through spring of 2008. DMI were measured for two weeks out of every six week period in first lactation on 44, 32, 29, and 13 HH, HJ, JH, and JJ cows. Daily milk and body weights and monthly milk components were collected. The National Research Council (NRC) DMI prediction equation was used across breed groups to investigate breed differences. DMI prediction equations were developed across breeds. Random regression model were used to predict energy consumed (TEC), energy needed for production, maintenance, and growth at every week of lactation (WOL). Energy balance (EB) was calculated at every WOL by subtracting energy for production, maintenance, growth, and pregnancy from TEC. Common health events were recorded if they occurred in the first 100 days of lactation. Logistic regression was used to analyze health disorder. The HJ and JH were not different from each other in any analyses. The NRC under-predicted DMI for HH and over-predicted DMI for HJ, JH, and JJ. There were significant breed differences in the prediction equations developed. Results indicated that breeds differ in DMI after accounting for production and body weights. The HH cows consumed more energy than HJ and JJ cows. The HH, HJ, and JJ were not different from each other for production but were different from JJ. The JH allocated less energy to maintenance than the HH. There were no breed differences for weeks required to reach positive EB, return to positive cumulative EB, or EB at week 21 of lactation. The HJ, JH, and JJ were more likely to have an incidence of mastitis than HH. The HJ and JH were less likely to have an incidence of metritis than HH. The results indicate breeds differ in DMI, and health diseases and evidence suggests differences in characterization of EB and warrants further investigation. / Ph. D.

Reproductive, maternal and weight traits were analyzed for Angus (A), Brahman (B), Hereford (H), and Nellore (N) straightbred cows; F1 NA; 3/8N 5/8A cows; and four breed composite cows (BANH) at the McGregor Research Station in Central Texas. Heterosis was estimated for calf crop born (CCB) (n = 1,698), calf crop weaned (CCW) (n = 1,698), calf survival (CS) (n = 1,388), birth weight (BW) (n = 1380), weaning weight (WW) (n = 1,198), and cow weight at palpation (PWT) (n = 1,929) by linear contrasts for cow breed and cow breed group. F1 NA and the quarter breed composite BANH dam group expressed significant (P < 0.0001) heterosis for calf crop born and calf crop weaned. The 3/8 N 5/8 Aa produced by matings of 3/4 A 1/4 N bulls to NA dams expressed significantly more heterosis for CCB (P < 0.0001) and CCW (P < 0.01), while the 3/8 N 5/8 Ac dams expressed less heterosis than predicted from the dominance model for both traits. For CS the 3/8 N 5/8 Aa expressed the same amount of heterosis as predicted from the dominance model of 0.05, while the 3/8 N 5/8 Ab and 3/8 N 5/8 Ac dams expressed less heterosis than predictions based on the dominance model. Heterosis estimates were only significantly higher (P < 0.10) for BANHb dams than expectations from the dominance model. For BW all the BANH cows expressed significant heterosis except for the BANH2 cows which expressed significant (P < 0.05) negative heterosis of -0.96 kg. Calves out of F1 NA cows were heaviest at weaning with 239 kg. All BANH cows expressed significant (P < 0.0001) heterosis for weaning weight except for the BANHc cows. These heterosis estimates were higher than those expected from the dominance model for BANHb and BANH2 cows, while the heterosis estimate was slightly lower in BANHa cows and similar for BANHc cows. All 3/8 N 5/8 A cows expressed less heterosis for WW than prediction from the dominance model. Nellore cows were the heaviest at four years of age with 542 kg. Only the BANHb and BANHc cows expressed significant (P < 0.05) heterosis for PWT. None of the 3/8 N 5/8 A cows expressed heterosis for cow weight at palpation. Results from this study showed that heterosis levels expressed by the different crossbred cow types were generally equal or higher to those predicted by the dominance model.

The objective of this study was to determine the onset of puberty by using progesterone profiles and anterior pituitary gonadotropin releasing hormone (GnRH) challenges in purebred and crossbred Holstein and Jersey heifers. In experiment 1, fifty prepubertal heifers by four sire - dam classifications (18 HH, 11 JJ, 10 JH, and 11 HJ) were used. The HH heifers attained puberty at an older age than the HJ, JH or JJ heifers, and these three classifications were not different from each other. There were significant differences in weight and wither height at puberty and average daily weight gain (ADWG) between all four sire - dam classifications. Season of birth had a significant effect on age and weight at puberty. In experiment 2, four prepubertal heifers from each sire - dam classification in experiment 1 were used at 3, 6, 9 and 12 mo of age to determine the effects of administering 200 μg GnRH on LH secretion. The effects of breed, age at challenge, and their interaction were only significant for time to LH peak. In conclusion, age at puberty in crossbred Holstein X Jersey heifers is regulated by breed and season of birth, and further research with larger sample sizes is needed to establish the relationship of pituitary maturation and the capacity to secrete LH in response to GnRH stimulation as related to onset of puberty in purebred and crossbred dairy heifers. / Master of Science

The purpose of this study was to determine empirically if crossbreeding offers a more profitable alternative to Utah cattlemen than vii straightbreeding. Ranchers practicing breed crossing were interviewed to determine the relative merits of crossbreeding and straightbreeding in the categories of calf crop, weaning weight, sale price, and minor economic factors under ranch conditions. Crossbred and straightbred sale prices \.,ere analyzed utilizing the records of the Smithfield Livestock Auction. Analysis of rancher interview data indicated that crossbred animals exceeded straightbreds in weaning weight and sale price. Crossbreds were further credited with lowering herd disease levels. No generalizations from comparative calf crop were feasible. Analysis of aucti.on data fo und no conclusive evidence of price differentiation between crossbreds and straightbreds.

Diss. (sammanfattning) Uppsala : Sveriges lantbruksuniversitet, 2008. / Härtill 4 uppsatser.

This degree has been obtained at the Faculty of Veterinary Science, Medical University of South Africa, now part of the new Faculty of Veterinary Medicine of the University of Pretoria Saanen and South African Indigenous goats were bred to kid at twelve months and annually thereafter. Milk production was recorded. Conception rates were generally more than 90 %, except for Indigenous goats in their first year. Few Indigenous goats (12 %) had twins at the first parturition, whereas 45% of Saanens had twins at 12 months of age. Twinning increased with age, and Saanen and Indigenous goats had kidding rates of 182% and 174% respectively in their third year, with Saanens later exceeding 200%. Triplets were infrequent, except in mature Saanens (9% of parturitions), and in Crossbreds (16%). Mean lactation yields were 579, 838, and 758kg for Saanens in first, second and third lactations, respectively. Lactation lengths were 283, 293 and 290 days respectively (excluding milk production beyond 300 days). Mean lactation yields for Crossbreds were 317, 446 and 438kg for first, second and third lactations. Lactation lengths were slightly shorter for Crossbreds than for the Saanens at 236, 248 and 257 days respectively. Indigenous goats were recorded at a mean milk yield of 23kg per lactation, and a mean lactation length of 94 days. Milk composition analyses for Saanens averaged 3.43, 2.88, and 4.49% for milk fat, protein and lactose, respectively. The analyses for Crossbred goats were 5.47, 3.88 and 4.81%, and for Indigenous goats were 9.33, 5.04 and 5.12%, respectively. These results showed that Crossbred goats gave less milk than Saanens, but significantly more than Indigenous goats. Milk production of Crossbred goats was found to be adequate for household requirements (subsistence purposes). In this way, the Crossbred goats were shown to be able to fulfil one of the objectives of the crossbreeding programme. The main disease identified was coccidiosis, acccompanied by pneumonia, which caused unacceptably high mortality among goat kids: 31% of Saanen, 24% of Crossbred, 38% of Three-quarter Saanen and 28% of Indigenous female kids. It is believed that this problem is largely management related, and worsened by overcrowding and the consequent poor hygiene; but the presence of rotavirus might also be significant. These aspects warrant further investigation. The main disease problem identified in mature goats was mastitis, which caused deaths of goats from peracute cases. Another important problem which became apparent after four years of age, was the incidence of squamous cell carcinoma on the udders of Saanens. Reduced exposure to the sun, by the provision of adequate shade should alleviate this problem; but the crossbreeding programme was seen to be of benefit, since no cases occurred in Crossbred goats. The experiment on heartwater aimed to assess resistance to this disease. Saanen, Indigenous and Crossbred goats were reared in a tick-free environment. In Year 1, eight goats of each type at eight months of age were given 5ml virulent heartwater blood of the Ball 3 stock. Temperatures and clinical sign were monitored. All eight Saanens were overcome by the disease, but only one Indigenous goat and two Crossbreds. In Year 2, Phase 1 of the experiment included six males and six females each of Indigenous and Crossbred goats at 11 months of age. Seven Crossbreds, but no Indigenous goats died. In Phase 2, nine Saanens were treated with tetracycline and compared to two untreated Saanens and nine untreated Three-quarter Saanen goats at 12 months of age. Both of the untreated and one of the treated Saanens died, and seven of the Three-quarter Saanens died. There were only small differences in temperature reactions; but Indigenous goats showed less clinical signs than other breeds. No differences of gender or year were apparent. These experiments indicated that Saanen goats show no genetic resistance, but that South African Indigenous goats appear to be genetically resistant to heartwater, and can transmit this resistance to a good proportion of Crossbred progeny. It has been shown therefore that it is feasible to develop a dairy goat resistant to heartwater, which could contribute significantly to the reduction of human malnutrition in rural and peri-urban communities in Southern Africa. / Dissertation (PhD)--University of Pretoria, 1997. / Production Animal Studies / unrestricted

Using terminal sires for crossbreeding is standard practice in the UK sheep industry, where over 70% of market lambs have terminal sire breeding. Thus, selection focusing on terminal sires will translate to changes in the entire industry. Consumers perceive lamb meat as fatty and demand for it has decreased. A lean growth index was developed for terminal sire breeds to increase carcass lean content while keeping fat constant at a constant age end point. The purposes of this study were: to evaluate the effects of index selection of terminal sires on their crossbred offspring up to harvest; to evaluate the effectiveness of the index within the terminal sire breeds; to evaluate the presence and consequences of heterogeneous environmental variances and genetics by environment interactions (GxE) on genetic evaluation. The most widely used breeds of terminal sires in the UK are Charollais, Suffolk, and Texel. These breeds participated in sire referencing schemes from the early 1990s by sharing rams selected on the lean growth index. From 1999 to 2002 approximately 15 high and 15 low lean growth index score rams per breed were selected from their sire referencing schemes and mated to Welsh and Scottish Mule ewes. Their crossbred offspring were reared on 3 farms in the UK under commercial conditions. In total, 6,515 lambs were born between 2000 and 2003. Lambs were weighed at birth (BWT), 5 weeks (5WT), and 10 weeks (10WT). The average daily gain (ADG) from birth to 10 weeks was calculated. Lambs were finished to an estimated 11% subcutaneous fat by visual examination. At harvest, they were weighed (HWT), ultrasonically scanned for muscle (UMD) and fat (UFD) depth, and assessed for condition score and conformation. Lambs sired by high index rams were on average, across breeds, heavier at all ages (P < 0.01) with 0.07 ± 0.03, 0.3 ± 0.1, 0.4 ± 0.1, and 1.2 ± 0.2 kg greater BWT, 5WT, 10WT, and HWT respectively. Their ADG was 5.1 ± 1.9 g/d greater than low index sired lambs. They had thicker UMD (0.7 ± 0.2 mm) and thinner UFD (0.08 ± 0.01 mm). High vs. low index sired lambs took the same amount of days to reach harvest fatness. Suffolk-sired lambs were on average heavier, with greater ADG, whereas Charollais-sired lambs were lightest with smallest ADG. Texel-sired lambs had thicker UMD than Charollais (0.7 ± 0.2 mm; P < 0.001) but were not different than Suffolk. Charollais-sired lambs had greater UFD than both Texel- (0.098 ± 0.016 mm) and Suffolk- (0.061 ± 0.017 mm) sired lambs (P < 0.001). Texel-sired lambs reached harvest condition faster than the other breeds (P < 0.01). Index selection produced heavier and leaner lambs at finishing. Producers have flexibility in choosing the terminal sire that best fits their production system. Heteroscedascity and GxE were found to be more important for ultrasonic traits than weight traits. Fitting a farm by sire random interaction component improved model fit, but only accounted for less than 2% of the variation in weight traits. For ultrasonic traits, it accounted for at least 10% of the variation. When fitting traits as separate but correlated by farm, genetic correlations among traits were mostly above 0.8, indicating no GxE. Reactions norms for sires were fitted. For weight traits and UMD, sires had positive slopes (were environmentally sensitive) that were similar in value, thus performance improved with improving environments. For UFD, reaction norm slopes varied form negative to positive, indicating GxE. Consequences of heteroscedasticity are not large for these data, and any consequence of GxE on breeding goals should be evaluated before explicitly modeling it in genetic evaluation. There was evidence of genetic variation in sensitivity of sires; therefore, they could be selected to be more or less sensitive depending on economic considerations. / Ph. D.

Thesis (MScAgric)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: Genetic selection for high milk production, type and appearance for the last 50 years has suppressed secondary traits such as reproductive performance, productive life, health and survivability in the pure milk breeds. The economic importance of these secondary traits in dairy production systems is the basis for the interest seen in crossbreeding. The problem of growth rate of heifers, cow fertility, reduced disease resistance and small body frame for beef production in Jerseys can be improved by crossing Jerseys with dual purpose breeds, such as Fleckviehs which possess a more beef potential. Against this background, this study aimed at comparing the production and reproduction of Jersey and Fleckvieh × Jersey cows in a pasture-based system. Milk recording was done according to standard milk recording procedures. Milk production (milk, fat, and protein yield) was adjusted to 305 days of lactation and corrected for age at calving. Effects of breed, parity, month and year were estimated for milk, fat and protein yield as well as fat and protein percentage using general linear models procedure. The fixed effects identified as having significant effects on milk, fat and protein yield were breed, parity and year. F×J cows produced significantly more milk than J cows (6141 ± 102 vs. 5398 ± 95 kg milk). Protein and fat yield were significantly higher in F×J (201 ± 3 and 272 ± 4 kg, respectively) than in J cows (194 ± 2 and 246 ± 3 kg, respectively). There percentages of fat and protein differed slightly between the two breeds with the Jersey recording slightly higher percentages (4.61 ± 0.04 and 3.62 ± 0.03 %, respectively) compared to the F×J cows’ percentages, which were, respectively, 4.47 ± 0.04 and 3.51 ± 0.03 %. It was concluded that F×J crossbred cows were more productive than purebred J cows probably owing to heterotic effects. Heifers were inseminated at 13 months of age and cows 40 days post-calving. Using insemination records and pregnancy check results, fertility traits were analyzed and compared between the two breeds, using analysis of variance for continuous records. Conception age was the same for both breeds resulting in a similar age at first calving. For cows, the interval from calving to first insemination was significantly shorter (P <0.001) in crossbred cows being 76.7 ± 2.2 days compared to 82.4 ± 2.5 days for purebreds. A larger proportion (P < 0.001) of 0.70 for crossbred cows was inseminated within 80 days after calving compared to 0.54 for J cows. Although the absolute number of days between calving and conception (DO) was lower for F×J cows in comparison to J cows (104.8 ± 6.8 vs. 114.8 ± 8.1days, respectively), the difference was not significant. However, the proportion of F×J cows confirmed pregnant by 100 days in milk was 0.79, which was higher (P < 0.001) than the 0.66 for J cows. Results indicate the potential of improving reproductive performance of J cows through crossing with dual-purpose breeds. The beef production of purebred J and Fleckvieh x Jersey (F×J) bull calves was compared, where bull calves were reared similarly for veal, i.e. carcass weight not exceeding 100 kg, or as steers for beef to 21 months of age. In both the veal and steer production systems, the mean birth weight were higher (P < 0.001) for crossbred in comparison to J calves and steers (33.5 ± 1.2 kg vs. 27.9 ± 1.2 kg for veal) and (33.4 ± 0.9 kg vs. 26.9 ± 0.9 kg for steers) respectively. The live weight at 6 months of age was 163.5 ± 3.9 kg for J bull calves, which was lower (P < 0.001) than that for F×J bull calves (180.6 ± 4.0 kg). The F×J bull calves had a significantly higher average daily gain (ADG) of 0.82 ± 0.02 kg/day compared to 0.73 ± 0.02 kg/day for J bulls. Marketing age differed (P < 0.001) in the veal production system with F×J and J bull calves marketed at 7.1 ± 0.1 and 6.3 ± 0.1 months, respectively. End live weight at 21 months of age was significantly higher (P < 0.001) in F×J bulls (441.4 ± 14.9 kg) than the 322.6 ± 13.4 kg in J bulls; while ADG differed (P < 0.001) between the two breeds being 0.64 ± 0.02 and 0.46 ± 0.0 kg/day in F×J and J bull calves, respectively. Crossbred steers had a significantly higher carcass of 206.5 ± 8.9 kg compared to 157.9 ± 8.6 kg for J steers. Results indicate the potential of improving beef production characteristics of the J cattle through crossbreeding. / AFRIKAANSE OPSOMMING: Genetiese seleksie vir hoë melkproduksie, tipe en voorkoms die afgelope 50 jaar het sekondêre eienskappe soos reproduksie, produktiewe lewe, gesondheid en oorlewing onderdruk in die suiwer melk rasse. Die ekonomiese belangrikheid van hierdie sekondêre eienskappe in melkproduksie stelsels is die basis vir kruisteling. Probleme soos groei tempo van verse, koei vrugbaarheid, verlaagde weerstandbiedenheid teen siektes en klein liggaam raam vir vleisproduksie in Jerseys kan verbeter word deur die kruising van Jerseys met ' n dubbele doel rasse, soos Fleckviehs wat beskik oor beter vleis potensiaal. Teen hierdie agtergrond, is hierdie studie daarop gemik om produksie en reproduksie van Jersey en Fleckvieh x Jersey koeie in 'n weiveld - gebaseerde stelsel te vergelyk. Melk opname is gedoen volgens standaard melkaantekening prosedures. Melkproduksie (melk-, veten proteïen opbrengs) was aangepas vir 305 dae van laktasie en gekorrigeer vir kalf ouderdom. ‘n Algemene lineêre model was gebruik om die effekte van ras, pariteit , maand en jaar op melk-, vet- en proteïen opbrengs sowel as vet- en proteïen persentasie te bepaal. Die vaste effekte geïdentifiseer met 'n beduidende effek op melk-, vet- en proteïen opbrengs was ras, pariteit en jaar. F × J koeie het aansienlik meer melk as J koeie (6141 ± 102 teen 5398 ± 95 kg melk) produseer . Vet opbrengs was aansienlik hoër in F × J koeie as in J koeie (272 ± 4 246 teen ± 3 kg vet). Proteïen opbrengs was ook aansienlik hoër in F × J koeie as J koeie (201 ± 3 vs 194 ± 2 kg proteïen). Vet en proteïen persentasies het geneig om effens te verskil met 'n klein effek (4.61 ± 0.04 % vet en 3.62 ± 0.03 % proteïen) vir J koeie en (4.47 ± 0.04 % vet en 3.51 ± 0.03 % proteïen) vir F × J koeie. Daar is tot die gevolgtrekking gekom dat F × J gekruisde koeie kan meer produktief wees as suiwer J koeie weens heterotiese effekte. Verse kunsmatig geïnsemineer was op 13 maande ouderdom en koeie 40 dae na- kalwing aangehou was. Met behulp van bevrugting en swangerskap rekords, is vrugbaarheid eienskappe ontleed en vergelyk tussen die twee rasse, met behulp van ontleding van variansie vir deurlopende rekords. Ouderdom van bevrugting was dieselfde vir beide rasse wat in 'n soortgelyke ouderdomsgroep was by eerste kalwing. Vir koeie was die interval van kalf tot eerste inseminasie aansienlik korter (P < 0.001) vir kruisgeteelde koeie wat 76.7 ± 2.2 dae in vergelyking met 82.4 ± 2.5 dae suiwerrasse is. ‘n Groter proporsie ( P < 0.001) van 0.70 vir gekruisteelde koeie is binne 80 dae na kalwing geïnsemineer in vergelyking met 0.54 vir J koeie. Alhoewel die absolute aantal dae tussen kalwing en opvatting (DO) laer was vir F × J koeie in vergelyking met J koeie (104.8 ± 6.8 teen 114.8 ± 8.1dae, onderskeidelik), is die verskil nie betekenisvol nie. Maar die verhouding van F × J koeie wat swanger bevestig is met 100 dae in melk was 0.79, wat hoër was (P < 0.001) is as die 0.66 vir J koeie. Resultate dui daarop dat daar potensiaal is reproduktiewe prestasie te verbeter van J koeie deur kruisteling met 'n dubbel- doel rasse. Die vleisproduksie van suiwer J en Fleckvieh x Jersey (F × J) bulkalwers vergelyk. Die bul kalwers is soortgelyk grootgemaak vir kalfsvleis, d.w.s karkas gewig mag nie 100 kg oorskry as bulkalwers nie, en as osse vir vleis tot 21 maande oud. In die kalwers- en os produksie stelsels, was die gemiddelde geboorte gewig hoër (P < 0.001) vir die kruise in vergelyking met J kalwers en osse (33.5 ± 1.2 kg teen 27.9 ± 1.2 kg vir kalwers) en (33.4 ± 0.9 kg vs . 26.9 ± 0.9 kg vir osse) onderskeidelik . Die lewendige gewig op 6 maande ouderdom was 163.5 ± 3.9 kg vir J bulkalwers en was hoër (P < 0.001) vir F × J bulkalwers 180.6 ± 4.0 kg. Die F × J bul kalwers het 'n aansienlik ‘n hoër gemiddelde daaglikse toename (GDT) van 0.82 ± 0.02 kg/dag in vergelyking met 0.73 ± 0.02 kg/dag vir J bulle. Bemarkingsouderdom verskil (P < 0.001) in die kalf produksie stelsel met F × J en J bulkalwers bemark op 7.1 ± 0.1 en 6.3 ± 0.1 maande , onderskeidelik. Finale lewendige gewig van 21 maande oud was aansienlik hoër 441.4 ± 14.9 kg in F × J bulle as 322.6 ± 13.4 kg in J bulle , terwyl GDT hoër was (P < 0.001), met 0.64 ± 0.02 kg/dag en 0.46 ± 0.0 kg/dag in F × J en J bulkalwers, onderskeidelik. Gekruisde osse het 'n aansienlik hoër karkasgewig 206.5 ± 8.9 kg in vergelyking met 157.9 ± 8.6 kg van J osse. Resultate dui daarop dat daar potensiaal is om die beesvleis produksie-eienskappe van die J beeste te verbeter d.m.v. kruisteling.

Submitted by Luciana Ferreira (lucgeral@gmail.com) on 2014-09-16T11:23:00Z No. of bitstreams: 2 Dissertacao2010_Ver__nica_Alves.pdf: 2047141 bytes, checksum: 188da6053334ff8142f1e9e0ec5f6e45 (MD5) license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5) / Approved for entry into archive by Luciana Ferreira (lucgeral@gmail.com) on 2014-09-16T13:35:47Z (GMT) No. of bitstreams: 2 Dissertacao2010_Ver__nica_Alves.pdf: 2047141 bytes, checksum: 188da6053334ff8142f1e9e0ec5f6e45 (MD5) license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5) / Made available in DSpace on 2014-09-16T13:35:47Z (GMT). No. of bitstreams: 2 Dissertacao2010_Ver__nica_Alves.pdf: 2047141 bytes, checksum: 188da6053334ff8142f1e9e0ec5f6e45 (MD5) license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5) Previous issue date: 2010-02-26 / Conselho Nacional de Pesquisa e Desenvolvimento Científico e Tecnológico - CNPq / The objective of this trial was to evaluate the productive and economic performance of dairy crossbred steers, reared on Brachiaria Brizantha pasture that received two levels of energetic supplementation during wet/dry transition and four levels during dry/wet transition seasons. During the wet season, forty-eight milk crossbred steers (Holstein x Zebu), with initial average weight of 123 kg and average age of 10 months were used. The treatments consisted of two levels of energy supplementation, 1% of BW, considered high, and 0.5% of BW, considered medium. During dry season, fortyfour fourteen-month-old milk crossbred steers (Holstein x Zebu) were used. The treatments consisted of two high levels of concentrate (1.6% and 1% of BW) and two medium levels of concentrate (0.8% and 0.5% of BW). The supplementation was composed of ground corn and mineral mixture, with urea addition during dry season. A completely randomized experimental design was used. The means were compared by F test at 5% probability in the first experiment and by Tukey test in the second one. The data were analyzed by SAS (1997). The average daily weight gain and final weight were similar between treatments in wet/dry transition. The thoracic measurement indicates a good ponderal development. Energetic supplementation of crossbred milk steers was economically viable, and the medium level (0.5% of BW) presented higher profitability than the high level (1% of BW). In dry season, the energy supplementation improved daily weight gain and the body measures of growing milk crossbred steers reared on pasture. Body length and scrotal perimeter indicated better body development. Milk crossbred steers supplemented on pasture with energy levels ranging from 0.5 to 1.6% should be commercialized for the price of live animal. And, in this case, the lowest level of supplementation (0.5% of BW) should be used for better profitability. / Objetivou-se avaliar o desempenho produtivo e econômico de novilhos de origem leiteira, suplementados com dois níveis de suplementação energética em pastagem de Brachiaria brizantha durante o período de transição águas/seca e a quatro níveis de suplementação energética durante o período de transição seca/águas. No período águas/seca foram utilizados 48 novilhos mestiços holandês x zebu, nãocastrados, com pesos médios iniciais de 123 kg e média de idade de 10 meses. Os tratamentos consistiram em dois níveis de suplementação energética, 1% do PV NA, considerado como nível alto e 0,5% do PV NM, considerado como nível médio. No período seca/águas foram 44 novilhos, não-castrados com 14 meses de idade e peso médio inicial de 183 kg. Os tratamentos consistiam de dois níveis altos de concentrado (1,6% e 1% do PV) e dois níveis médios de concentrado (0,8% e 0,5% do PV). O suplemento fornecido era composto por fubá de milho e mistura mineral. Na seca/águas adicionou-se uréia no suplemento. Utilizou um delineamento inteiramente casualizado e as médias foram comparadas pelo teste F para o primeiro experimento e Teste Tukey no segundo. Os dados foram analisados pelo SAS (1997). O ganho de peso médio diário e peso final foram similares entre tratamentos na transição águas/seca. Perímetro torácico representou bom indicativo de desenvolvimento ponderal. A suplementação energética de bovinos mestiços de origem leiteira mostrou-se economicamente viável, sendo que o nível médio (0,5% do PV) apresentou lucratividade superior comparado com o nível alto (1% do PV). No período seca/, a suplementação energética melhorou o ganho em peso e as medidas corporais de bovinos mestiços de origem leiteira em crescimento mantidos a pasto. Perímetro escrotal e comprimento representaram bom indicativo de desenvolvimento ponderal. Mestiços de origem leiteira suplementados a pasto com níveis variando de 0,5 a 1,6% de suplementação energética devem ser comercializados pelo preço de animal vivo. E quando a comercialização for feita dessa forma, recomenda-se utilizar o menor nível de suplementação (0,5% do PV) para se obter maior lucratividade.

O efeito da heterose na produção de leite é de suma importância nos cruzamentos obtidos entre animais de raças europeias e zebuínas. Contudo, são inexistentes pesquisas que comprovem o efeito da heterose sobre os componentes da curva de lactação nos diferentes grupos genéticos da raça Girolando. Objetivou-se utilizar diferentes modelos matemáticos para melhor descrever a curva de lactação a fim de avaliar o efeito de heterose sobre os componentes da curva de lactação dessa população, bem como avaliar o impacto da inclusão do efeito da heterose no modelo sobre as estimativas de parâmetros genéticos para produção de leite até 305 dias obtidas via método REML. Os modelos linear e não linear de Wood, Wilmink e Ali e Shaeffer foram ajustados aos registros produtivos de controles mensais, para posterior estimar forma individual e conjunta (média), o pico de lactação, tempo ao pico, persistência, produção total de leite até 305 dias e os parâmetros específicos dos modelos relacionados com curva de lactação (produção inicial e taxa de decréscimo da produção). Na comparação de todos esses modelos matemáticos quanto à qualidade de ajustamento foram utilizados os critérios RMSE, AIC e BIC No geral, observou-se que a qualidade de ajuste dos modelos diferiu conforme o grupo genético. Foi observado efeito de heterose (P<0,001) para a maioria dos componentes que compõem a curva de lactação, com exceção de algumas medidas de persistência. Dentre os componentes da curva de lactação, o pico de lactação foi o que apresentou efeito de heterose mais expressivo, explicando parcialmente a heterose (20% a 23%) observada na produção de leite até 305 dias. As estimativas de herdabilidade para a produção de leite até 305 dias ajustada ou não pelos modelos matemáticos não lineares quase não variaram (0,14 à 0,20). Verificou-se ainda que a maioria dos grupos genéticos apresentaram efeito de heterose para a produção de leite até 305 dias, porém os maiores efeitos ocorreram em vacas 1/2H com 1112,73 kg a mais em relação à média de seus pais puros. Assim, pode se concluir que os benefícios da heterose para a raça Girolando são evidentes e mostram ser mais relacionados com os componentes da fase inicial da curva da lactação refletindo na expressão da heterose para a produção de leite até 305 dias, principal característica da atividade leiteira. / The effect of heterosis on milk yield is fundamental in cross breeding between European breeds and zebu. However, there is a lack of studies on the heterosis effect of the components of lactation curve in the different crossbred genetic groups of Girolando Cattle. The objective was to use different mathematical models to better describe the lactation curve in order to evaluate the effect of heterosis on the components of the lactation curve of this population, as well as to evaluate the impact of the inclusion of the heterosis effect in the model on the estimation of the genetic parameters for 305-day milk yield obtained by REML method. Wood’s, Wilmink’s, and Ali and Shaeffer’s models were fitted to the monthly test day milk yield records, to estimate individual and joint (average) shape, peak yield, time to peak, persistency, 305-day milk yield and the specific parameters of the models associated to the lactation curve (initial stage of lactation and rate of decrease of production). RMSE, AIC, and BIC criteria were used in order to compare the quality of fit of the different mathematical models. In general, the quality of fit of the models differed in the genetic groups The effect of heterosis was significant (P <0.001) for most of the components that of the lactation curve, with the exception of some measures of persistency. Among the components of the lactation curve, the peak of lactation presented the most expressive heterosis effect, which partially could explain the heterosis (20% to 23%) on 305-day milk yield. Estimates of heritability for 305-day milk yield presented a low variation (0.14 to 0.20). Most of the groups presented heterosis effect for 305-day milk yield, but the highest effects were on 1/2H cows. The 305-day milk yield of 1/2H was 1112.73 kg higher than that in the average between parental pure breeds. Thus, it can be concluded that the benefits of heterosis to the Girolando breed are evident. The heterosis is associated to the components of the initial stage of the lactation curve, which is reflected in the expression of heterosis for 305-day milk yield, the most important trait of economic interest in Brazil.