M. Valencia-Posadas

Genetic and environmental parameters for milk production, udder health, and fertility traits in Mexican Holstein cows

Genetic and phenotypic parameters for Mexican Holstein cows were estimated for first- to third-parity cows with records from 1998 to 2003 (n=2,971-15,927) for 305-d mature equivalent milk production (MEM), fat production (MEF), and protein production (MEP), somatic cell score (SCS), subsequent calving interval (CAI), and age at first calving (AFC). Genetic parameters were obtained by average information matrix-REML methodology using 6-trait (first-parity data) and 5-trait (second- and third-parity data) animal models. Heritability estimates for production traits were between 0.17+/-0.02 and 0.23+/-0.02 for first- and second-parity cows and between 0.12+/-0.03 and 0.13+/-0.03 for third-parity cows. Heritability estimates for SCS were similar for all parities (0.10+/-0.02 to 0.11+/-0.03). For CAI, estimates of heritability were 0.01+/-0.05 for third-parity cows and 0.02+/-0.02 for second-parity cows. The heritability for AFC was moderate (0.28+/-0.03). No unfavorable estimates of correlations were found among MEM, MEF, MEP, CAI, and SCS. Estimates of environmental and phenotypic correlations were large and positive among production traits; favorable between SCS and CAI; slightly favorable between MEM, MEF, and MEP and SCS, between AFC and SCS, and between SCS and CAI; and small but unfavorable between production traits and CAI. Estimates of genetic variation and heritability indicate that selection would result in genetic improvement of production traits, AFC, and SCS. Estimates of both heritability and genetic variation for CAI were small, which indicates that genetic improvement would be difficult.

Breed differences over time and heritability estimates for production and reproduction traits of dairy goats in the United States

To aid in improvement of breeding programs for production and reproduction traits of US dairy goats, breed differences over time were documented and genetic parameters were estimated. Data were from herds with ≥2 breeds (Alpine, LaMancha, Nubian, Oberhasli, Saanen, or Toggenburg), but only purebred data were analyzed. Three kidding periods were examined: 1976 through 1984, 1985 through 1994, and 1995 through 2005. Univariate repeatability mixed models were used to estimate least squares means by kidding period-breed and genetic parameters for milk, fat, and protein yields, combined fat and protein yield, fat and protein percentages, protein:fat ratio, age at first kidding, and kidding interval. Trends across kidding periods were favorable for most yield traits for all breeds but generally unfavorable for reproduction traits. Saanens had the highest milk (1,063 to 1,125 kg) and protein yields (31 to 33 kg). Nubians had the highest fat yields (37 to 40 kg) and lowest milk yields (791 to 851 kg). Oberhaslis had the lowest fat (31 to 33 kg) and protein (23 to 27 kg) yields. Alpines had the largest increase in milk yield (7.4%); Oberhaslis had the largest increase in protein (17.4%) and combined fat and protein (13.2%) yields. Combined fat and protein yield was higher for Nubians, Saanens, and Alpines (65 to 72 kg) than for LaManchas, Toggenburgs, and Oberhaslis (53 to 67 kg). Nubians had the highest fat (4.7 to 4.8%) and protein (3.6 to 3.8%) percentages. Only Nubians increased in fat percentage (2.1%); protein percentage increased most for Toggenburgs (7.4%) and Alpines (7.1%). Protein:fat ratio was highest for Toggenburgs (0.84 to 0.89) and lowest for Nubians (0.76 to 0.81), but Nubians had the largest increase in protein:fat ratio (6.6%). Saanens were oldest at first kidding (509 to 589 d), and Toggenburgs and LaManchas generally were youngest (435 to 545 d); age at first kidding increased most for Alpines (21.8%) and LaManchas (21.6%). Kidding intervals generally were shorter for Oberhaslis, LaManchas, and Nubians (350 to 377 d) than for Toggenburgs, Alpines, and Saanens (373 to 387 d). Kidding interval increased most for Nubians (3.9%) and Saanens (3.8%) and decreased only for Oberhaslis (5.4%). Heritability estimates across breeds were 0.35 for milk and fat yields, 0.37 for protein yield and protein:fat ratio, 0.36 for combined fat and protein yield, 0.52 for fat percentage, 0.54 for protein percentage, 0.23 for age at first kidding, and 0.05 for kidding interval. Genetic selection within breed is feasible for production and reproduction traits of US dairy goats.

Short communication: Genetic and environmental relationships between milk yield and kidding interval in dairy goats

First-parity 305-d milk yield and intervals between first and second kiddings from 1975 through 2005 were analyzed to estimate genetic and environmental parameters for United States Alpine, LaMancha, Nubian, Saanen, and Toggenburg dairy goats. The data set included 43,612 does with first-parity milk yield and 25,863 does with first kidding interval. Parameters were estimated by REML using bivariate mixed models within and across breeds. Fixed effects were month and herd-year of kidding within breed and month and breed-herd-year of kidding across breeds. Random effects were animal and residual. The heritability estimate for first-parity milk yield was 0.36+/-0.01 across breeds and ranged from 0.35 to 0.38 within breed; heritability for first kidding interval was 0.05+/-0.01 across breeds and ranged from 0.00 to 0.15 within breed. The estimate of the genetic correlation between first-parity milk yield and first kidding interval was positive (unfavorable) across breeds (0.35+/-0.09). Estimates of environmental correlations within and across breeds were positive (0.16-0.25). The presence of unfavorable genetic relationships between milk yield and kidding interval indicates a need to include reproductive performance as a selection criterion.

Molecular Detection and Sensitivity to Antibiotics and Bacteriocins of Pathogens Isolated from Bovine Mastitis in Family Dairy Herds of Central Mexico

Thirty-two farms (n = 535 cows) located in the state of Guanajuato, Mexico, were sampled. Pathogens from bovine subclinical mastitis (SCM) and clinical mastitis (CLM) were identified by 16S rDNA and the sensitivity to both antibiotics and bacteriocins of Bacillus thuringiensis was tested. Forty-six milk samples were selected for their positive California Mastitis Test (CMT) (≥3) and any abnormality in the udder or milk. The frequency of SCM and CLM was 39.1% and 9.3%, respectively. Averages for test day milk yield (MY), lactation number (LN), herd size (HS), and number of days in milk (DM) were 20.6 kg, 2.8 lactations, 16.7 animals, and 164.1 days, respectively. MY was dependent on dairy herd (DH), LN, HS, and DM (P < 0.01), and correlations between udder quarters from the CMT were around 0.49 (P < 0.01). Coagulase-negative staphylococci were mainly identified, as well as Staphylococcus aureus, Streptococcus uberis, Brevibacterium stationis, B. conglomeratum, and Staphylococcus agnetis. Bacterial isolates were resistant to penicillin, clindamycin, ampicillin, and cefotaxime. Bacteriocins synthesized by Bacillus thuringiensis inhibited the growth of multiantibiotic resistance bacteria such as S. agnetis, S. equorum, Streptococcus uberis, Brevibacterium stationis, and Brachybacterium conglomeratum, but they were not active against S. sciuri, a microorganism that showed an 84% resistance to antibiotics tested in this study.

Estimation of genetic parameters for productive life, reproduction, and milk-production traits in US dairy goats

Heritabilities and correlations for milk yield (MY), fat yield (FY), protein yield (PY), combined fat and protein yield (FPY), fat percentage (F%), protein percentage (P%), age at first kidding (AFK), interval between the first and second kidding (KI), and real and functional productive life at 72mo (FPL72) of 33,725 US dairy goats, were estimated using animal models. Productive life was defined as the total days in production until 72mo of age (PL72) for goats having the opportunity to express the trait. Functional productive life was obtained by correcting PL72 for MY, FY, PY, and final type score (FS). Six selection indexes were used, including or excluding PL72, with 6 groups of different economic weights, to estimate the responses to selection considering MY, FY, PY, and PL72 as selection criteria. The main criteria that determined the culling of a goat from the herd were low FS, MY, and FY per lactation. Heritability estimates were 0.22, 0.17, 0.37, 0.37, 0.38, 0.39, 0.54, 0.64, 0.09, and 0.16 for PL72, FPL72, MY, FY, PY, FPY, F%, P%, KI, and AFK, respectively. Most genetic correlations between the evaluated traits and PL72 or FPL72 were positive, except for F% (-0.04 and -0.06, respectively), P% (-0.002 and -0.03, respectively), and AFK (-0.03 and -0.01, respectively). The highest genetic correlations were between FPL72 and MY (0.39) and between PL72 and MY (0.33). Most phenotypic correlations between the traits evaluated and FPL72 and PL72 were positive (>0.23 and >0.26, respectively), except for F% (-0.004 and -0.02, respectively), P% (-0.05 and -0.02), KI (-0.01 and -0.07), and AFK (-0.08 and -0.08). The direct selection for PL72 increased it by 102.28d per generation. The use of MY, FY, PY, KI, or AFK as selection criteria increased PL72 by 39.21, 27.33, 35.90, -8.28, or 2.77d per generation, respectively. The inclusion of PL72 as selection criterion increased the expected response per generation from 0.15 to 17.35% in all selection indices studied.

Breed and breed × environment interaction effects for growth traits and survival rate from birth to weaning in crossbred lambs1

This study was conducted to estimate the effects of sire breed (Charollais, Dorper, Dorset, Hampshire, and Suffolk) and genetic group of the dam [local whiteface (Criolla), grade Hampshire, grade Suffolk, F(1) Dorper × Pelibuey, Australian composite, hair sheep (Barbados Blackbelly or Pelibuey), Dorset, Hampshire and Suffolk] on birth weight, survival rate from birth to weaning, and weaning weight adjusted to 65 d of age. Data were recorded from 2004 to 2006 on crossbreed lambs obtained by artificial insemination from 114 flocks in Central Mexico. High (above the mean) or low (below the mean) environmental categories were assigned to each record from flock-year-season effects solutions obtained in fixed-effects linear model analyses. Birth weights of lambs sired by Charollais rams (3.94 kg) were heavier (P < 0.05) than those sired by Suffolk (3.69 kg) whereas Dorper-, Dorset-, and Hampshire-sired lambs were intermediate. For weaning weight, lambs sired by Charollais were the heaviest (19.16 kg) compared with lambs sired by Hampshire (17.86 kg), Suffolk (17.79 kg), and Dorper (17.28 kg) whereas Dorset sired were the lightest (16.77 kg; P < 0.05). Lambs sired by Dorset rams had a lower survival rate (77.1%) than lambs sired by Charollais, Dorper, Hampshire, or Suffolk (81.6 to 83.3%; P < 0.05). Lambs from Australian composite, Dorset, Hampshire, and Suffolk dams were heavier for birth and weaning compared with lambs from local whiteface (Criolla), hair sheep breeds (Barbados Blackbelly or Pelibuey), or crosses (F(1) Pelibuey × Dorper) dams (P < 0.05) whereas lambs from grade Hampshire and grade Suffolk were intermediate. The genetic group of the dam had no effect (P > 0.05) on survival rate. Sire breed × environmental category interaction effect was significant for birth weight (P < 0.01) and weaning weight (P < 0.05), but relatively small changes on the ranking of sire breeds were observed between environmental categories for weaning weight. Genetic group of the dam × environmental category interaction effect was significant for birth and weaning weights (P < 0.01). Weaning weight of lambs from hair sheep breeds (Barbados Blackbelly or Pelibuey) and crosses (F(1) Pelibuey × Dorper) as well as purebred Dorset, Hampshire, and Suffolk dams were more affected when changing from the high to the low environmental category compared with the other genetic groups. No breed of the sire or genetic group of the dam × environmental category interactions were (P > 0.05) observed for survival rate.

Linear and nonlinear genetic relationships between type traits and productive life in US dairy goats

Linear or nonlinear genetic relationships between productive life and functional productive life at 72 mo, with final score (SCO), stature, strength, dairyness (DAI), teat diameter, rear legs (side view), rump angle, rump width (RUW), fore udder attachment (FUA), rear udder height, rear udder arch, udder depth (UDD), suspensory ligament (SUS), and teat placement, as well as heritabilities and correlations were estimated from multibreed US dairy goat records. Productive life was defined as the total days in production until 72 mo of age (PL72) for goats having the opportunity to express the trait. Functional productive life (FPL72) was analyzed by incorporating first lactation milk yield, fat yield, protein yield, and SCO in the statistical model. Heritabilities and correlations were estimated using linear mixed models with pedigree additive genetic relationships and ASReml software. Nonlinearity of genetic relationships was assessed based on second-degree polynomial (quadratic) regression models, with the breeding values of PL72 or FPL72 as responses and the breeding values for each type trait (linear and quadratic) as predictor variables. Heritability estimates were 0.19, 0.14, 0.18, 0.20, 0.14, 0.07, 0.28, 0.20, 0.15, 0.13, 0.25, 0.18, 0.20, 0.21, 0.21, and 0.32 for PL72, FPL72, SCO, stature, strength, DAI, teat diameter, rear legs, rump angle, RUW, FUA, rear udder height, rear udder arch, UDD, SUS, and teat placement, respectively. The type traits SCO, RUW, and FUA were the most correlated with PL72 and FPL72, so these may be used as selection criteria to increase longevity in dairy goats. An increase in the coefficient of determination >1% for the second degree, compared with that for the linear model for either PL72 or FPL72, was taken as evidence of a nonlinear genetic relationship. Using this criterion, PL72 showed maximum values at intermediate scores in DAI, UDD, and RUW, and maximum values at extreme scores in FUA and SUS, whereas FPL72 showed maximum values at intermediate scores in DAI and UDD, and maximum values at extreme scores in FUA, RUW, and SUS. Selecting for increased SCO, RUW, and FUA will lead to an increase of FPL72 in goats. Consideration of nonlinear relationships between DAI, FUA, RUW, SUS, and UDD may help in the design of more efficient breeding programs for dairy goats using conformation traits.

Additive and dominance effects of the αs1-casein locus on milk yield and composition traits in dairy goats

The objective of this study was to evaluate the effects of the CSN1S1 locus polymorphism on 305-d records of milk, fat, protein, lactose and total solids yields, fat, protein, lactose and total solids contents in Mexican dairy goats. A total of 514 lactation records belonging to Alpine (n=60), Saanen (n=105) and Toggenburg (n=74) goats, born from 2003 to 2006 in three herds were used. Discrimination between alleles E, F, N, A* (CSN1S1 A, G, H, I, O1 and O2) and B* (CSN1S1 B1, B2, B3, B4, C and L) were made by amplification of fragments of the gene CSN1S1 and digestion with the restriction endonuclease XmnI. In order to estimate additive and dominance effects, data sets including (1) all genotypes, and (2) only homozygote genotypes, were analysed using linear mixed models. The allele A*, had significant additive effects for protein content (0·21±0·07%; P=0·002) and total solids content (0·66±0·23%; P=0·005) when compared with allele F. An unfavourable additive effect of allele A* on milk yield was found in the Alpine breed (-81·4±40·2; P=0·046) when compared with allele F. Favourable dominance effects were found for some genotypes (P<0·05) for milk yield (A*N and B*N), fat yield (A*N and B*E), protein yield (A*N and B*E), lactose yield (A*N) and total solids yield (A*N). Also, unfavourable dominance effects were found (P<0·05) for protein content (A*B* and A*N) and total solids content (A*B*, A*N, and A*F). Allele A* was the only one with a positive effect for protein content. Significant allele-year interaction effects were also observed. The presence of significant dominance effects, estimated between specific pairs of alleles, challenged the purely additive nature of the genetic effect at the CSN1S1 locus. Implications from use of CSN1S1 effects in goat breeding programmes are presented.

Antibiotic susceptibility of Staphylococcus aureus isolated from subclinical bovine mastitis cases and in vitro efficacy of bacteriophage

Staphylococcus aureus is an opportunistic pathogen that may cause severe infections in livestock, and represents the major cause of mastitis in dairy cows. Currently, instead of using antibiotics, new strategies are sought to reduce this clinical health problem. The aim of this study was to determine the efficacy of phage therapy to kill S. aureus strains obtained from farms located at the State of Guanajuato, México. Thirty-six S. aureus strains from cow milk with subclinical mastitis were isolated and identified, and the susceptibility to antibiotics and four phages also isolated in this work was tested. It was found that more of 90% of S. aureus isolates were not susceptible to six or more antibiotics, and 100% were resistant to penicillin, dicloxacillin, cefotaxime, ampicillin and cephalothin, and 81 and 77%, to tetracycline and cefuroxime, respectively. Fortunately, 100% of S. aureus isolates were susceptible to phages used in this work, which was detected as clear zones using specific phage. It was shown for the first time, that phages used in this study are active against pathogenic S. aureus and might be incorporated into the therapy as an important tool for the control of staphylococcal bovine mastitis, specially to antibiotic-resistant S. aureus strains isolated in farm located at the state of Guanajuato, México; and its use might be extended to other regions inside or outside the country.