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Item Improving the performance of Mpwapwa breed cows in Tanzania : a fertility management approach : a thesis submitted in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Veterinary Science at Massey University, School of Veterinary Science, Manawatu(Massey University, 2024-12-12) Kabuni, Kabuni ThomasBeef cattle farming is an important part of Tanzania’s economy being widespread throughout Tanzania. It is commonly practiced by small-scale farmers, often in conjunction with other agricultural and commercial activities. As part of the colonial government’s efforts to develop agriculture in Tanzania in the 1940’s, the Mpwapwa breed was developed, largely from Bos indicus stock, as a dual-purpose breed to provide better beef and milk production. The Mpwapwa TALIRI research centre, in the Dodoma region of Tanzania, maintains a nucleus herd of Mpwapwa cattle from which it has provided breeding stock and, prior to 1973, an artificial insemination (AI) program to farmers. These programs fell into abeyance during the post-colonial era. Critically, the AI service was discontinued until TALIRI Mpwapwa started to re-equip its facilities in 2018. The major limiter to re-establishing the AI service has been the high cost and poor availability of liquid nitrogen, which means that it is not feasible to develop a service that is dependent on cryopreserved semen. In the past globally, and in New Zealand currently, bovine AI services have been based upon chilled or ambient temperature (AT) diluents, so the feasibility of developing a new AI service for Mpwapwa cattle using ambient-temperature semen was investigated. Most of the use of AT diluents has been in temperate climates, so an important component of re-establishing the AI service was to determine whether AT diluents could sustain sperm viability at the high (>30oC) temperatures that pertain in Tanzania. The first step was to survey farmers who kept Mpwapwa cattle about their management and breeding practices using a cross-sectional survey. This was undertaken to determine whether they were interested in an AI program for their cattle and whether they thought it would be a useful method of breeding for their cattle. A survey was administered across 100 farmers in the Mpwapwa region. Median herd size was 7 (range 1-150) and median farm size was 12 acres (0.4-500), milk yields were generally under 5 L/cow/day and carcass weights were typically 112-142 kg. The Mpwapwa breed was regarded as better than other local breeds. Only 17 farmers had used AI, almost always after single-PGF2α synchronisation. However, 69 farmers who had not used AI were interested in doing so and 61 considered that AI was better than natural bull mating being aware of the significant of AI on livestock breeding. The conclusions from the survey were that an AI service would have to be tailored around small herds, probably with fixed-time AI (FTAI) after single-PGF2α synchronisation, and would have to offer farmers significant improvements in animal genetics and fertility and/or easier management of breeding than at the present. As the Mpwapwa bulls had never been evaluated to determine whether their semen was of adequate quality to use in an AI service, the next step was to undertake breeding soundness examination (BSE) of the bulls in the TALIRI Mpwapwa stud. The 53 heaviest bulls out of the total stud of 120 were subjected to a full BSE including semen examination (collection by electroejaculation). Scrotal circumference was similar in bulls that were 24-36 months old (mean: 27.1 cm, SD: 1.6 cm) and those that were >36 months old (mean: 27.8 cm, SD: 2.0 cm). Semen was successfully collected from 44 bulls. Mean ejaculate volume was 5.5 mL (SD: 2.7 mL). Only 4 bulls did not have ≥75% morphologically normal sperm. Mean ejaculate density was relatively low at 303 x106 sperm/mL (range: 57-966, SD: 258 x106 sperm/mL). Density was >400 x106/mL in 31 bulls, >700 x106/mL in 2 bulls and >800 x106/mL in 6 bulls. These 8 bulls were considered suitable for use in an AI program. The variation of semen quality was largely as expected for a breed that had not been subjected to any form of selection for breeding ability. Findings for these Mpwapwa breed bulls largely align with those of similar low body-weight breeds of B. indicus that are found in East Africa and South-East Asia, but are significantly less than would be expected from the improved indicus breeds of South America, Australia and southern Africa. DNA fragmentation was examined in the same 53 bulls, again, as the status of these hitherto unselected bulls was unknown. Most bulls had unfragmented sperm (mean: 94.7%, SD: 6.8, Mode: 100%), with only 5 bulls having <90% normal sperm. Fragmentation was therefore not sufficiently widespread in the bull stud to cause concern about their use in AI. The next step was to assess the survival of sperm at ambient temperatures. Ejaculates from 35 bulls were diluted 1:1 in Tris-egg yolk (TE), Optixcell and coconut water, loaded into 0.25 mL mini- straws and incubated in water baths at 20°C, 27°C and 33°C (Year 1) or 8°C, 17°C and 33°C (Year-2). Motility was evaluated using computer-assisted analysis after 6, 24, 48, 72 and 120 h. Sperm survival was related to temperature, such that survival at 8°C was better than at other temperatures. Survival in coconut water was poor, with limited survival even at 24 h. Mean survival at 72 h was <40% in both TE and Optixcell, but was >40% at 48 h except at 32oC. These results suggested that storage at <20oC for up to 48 h would give acceptable motility (i.e. ≥50%) for use in AI. Sperm from some (n=4) individual bulls survived, however, for up to 120 h at 8oC and from 2 bulls at 17oC. Semen from 3 bulls survived for 120 h at 32oC. These results showed that storage for 48 h at 17°C in TE or Optixcell was feasible for most bulls, and individuals could be identified whose semen survived longer and/or at higher temperatures for at least 72 h. Thus, maintaining semen at ambient temperatures of 32°C was difficult for >24 h, but was readily achievable in an AT diluent with a modest amount of cooling for 48 h. This survival would permit an AI service based on AT semen, provided inseminations could be performed soon after collection, or after a period of modest refrigeration. Finally, a proof-of-concept AI trial was undertaken, in which 303 cows were inseminated with cryopreserved or AT semen after a double-PGF2α synchronisation (to detected oestrus after PGF2α- 1 and by FTAI after PGF2α-2). Conception rates to AI were 62% to AT and 38% to cryopreserved semen (final pregnancy rates were 99% and 97% respectively after 12 weeks of bull mating). Whilst the trial was not undertaken to demonstrate that one method was superior to the other, it did demonstrate that FTAI with AT semen was at least as good as with cryopreserved semen. In terms of developing an AT AI service, this thesis has shown that it would likely be well-received by smallholder farmers, that there is a cohort of bulls which are of satisfactory breeding quality for use in AI, that their semen survives for long enough for AT semen to be the basis of an AI service, and that results to FTAI are at least as good as with cryopreserved semen. In summary, the protocol itself is cost-effective and, as such, it could be used within the Tanzanian beef cattle breeding programmes. Being simple to schedule should make it easily accessible and implementable by poor smallholder farmers in the Mpwapwa region and, hence more accessible than other expensive protocols with more hormones. Even compared to natural mating, the costs of AT AI are still cheaper, making it more affordable than the costs of buying and managing a high genetic merit Mpwapwa bull. Wider screening of bulls for those whose semen survives longer and/or at higher ambient temperatures would allow for the selection of bulls with the highest quality semen. Addition of a limited degree of refrigeration (maintaining semen at 15-20oC) would allow more flexibility to the AI collection/processing centre.Item Lactation curves of Montbéliarde-sired and Viking Red-sired crossbred cows and their Holstein herdmates in commercial dairies(Elsevier Inc. on behalf of the American Dairy Science Association, 2024-06) Houdek ES; Hazel AR; Lopez-Villalobos N; Hansen LB; Heins BJLactation curves were estimated for Montbéliarde (MO) × Holstein (HO) and Viking Red (VR) × HO 2-breed crossbred cows and for MO × VR/HO and VR × MO/HO 3-breed crossbred cows and their HO herdmates from test-day observations in 7 high-performance herds that participated in a designed study. Cows calved from 2010 to 2017. Test-day observations from milk recording were used to fit the lactation curves of cows in their first 3 lactations. Lactations of cows were required to have at least 250 DIM and to have at least 6 test days ≤265 DIM. Lactation curves from random regression (RR) were compared for 305-d production (kg), peak production (kg), peak day of production, and production from 4 to 103 DIM (kg), from 104 to 205 DIM (kg), and from 206 to 305 DIM (kg) for milk, fat, and protein. Also, the persistency of production was compared. First-lactation versus second- and third-lactation cows were analyzed separately for both the 2-breed and 3-breed crossbred cows and their respective HO herdmates. Legendre polynomial RR had the best goodness of fit for the lactation curves compared with Ali-Schaeffer and Wilmink RR from the test-day observations of milk, fat, and protein production. For fluid milk production of first-lactation cows, the MO × HO 2-breed crossbreds were not different from their HO herdmates for any of the lactation-curve characteristics, except persistency. However, the VR × HO 2-breed crossbreds had less fluid milk production compared with their HO herdmates. For first lactation, the MO × HO 2-breed crossbreds had more persistency of milk, fat, and protein production compared with their HO herdmates. The first-lactation MO × VR/HO 3-breed crossbreds had more persistency of fluid milk production compared with their HO herdmates. For second and third lactations, both the MO × HO and the VR × HO 2-breed crossbreds had higher fat production compared with their HO herdmates. Furthermore, the MO × HO 2-breed crossbreds had more protein production (kg) in all 3 periods of lactation compared with their HO herdmates. Crossbred cows may have advantages over HO cows for persistency of production in high-performance herds.Item Investigations on black soldier fly (Hermetia illucens L.) production and nutrition : a sustainable solution for poultry feeding : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Animal Science, School of Agriculture and Environment, College of Sciences, Massey University, Palmerston North 4442, New Zealand(Massey University, 2024-08-20) Mahmoud, Amira Elsayed AbdallaBlack soldier fly (BSF; Hermetia illucens L.) is renowned for efficiently converting organic wastes into valuable biomass rich in protein and fat. This makes it a profitable and sustainable method for waste management and a useful feed source for animals like poultry, fish, pigs, and pets. Using BSF reduces the dependence on traditional feed ingredients such as soybean and fish meal, which are often imported and add to the carbon footprint. Despite growing interest and large-scale production of BSF meals, knowledge gaps hinder the widespread adoption of this technology, especially in small and medium-scale operations. The overall aim of this multidisciplinary research was to better understand the biology and rearing methods of BSF, processing of insect meals, and their utilisation by broiler chickens. The thesis research specifically investigated: (1) methods and techniques that optimise BSF breeding and meal processing relevant to small and medium-sized operations, (2) the impact of substrate type, moisture, and compaction on the non-feeding stages of BSF, (3) disease management in BSF colonies to ensure healthy population dynamics, including the first record of red mites as a parasitic case within BSF colonies, and (4) the nutritional value of the larval and pre-pupal stages of BSF as replacements for soybean meal (SBM) in poultry feeds. Firstly, the thesis provided a practical guide to establishing and managing a BSF colony, covering the entire process from egg production to larval and pre-pupal meal processing. The procedures were based on the experience of producing 450 kg of BSF larvae (BSFL) and pre-pupae (BSFP) over the course of doctoral research. Secondly, a study examined the impacts of substrate type, moisture levels, and compaction on BSF pupation success, adult emergence and morality. Among the six substrates evaluated (sand, wood shavings, topsoil, vermiculite, spent wheat middlings, and potting soil), spent wheat middlings presented as the most cost-effective and readily available option. Moisture level was found to significantly affect substrate performance, with 10% moisture providing the best outcomes for pupation and reducing mortality while avoiding mould growth. Mild compaction did not negatively impact pupation development, suggesting that moderate compaction could enable small farmers to reuse substrate and lower the cost. Thirdly, an infestation of poultry red mites (Dermanyssus gallinae), causing noticeable skin discoloration and anatomical damage to the BSFL and BSFP, was identified. The mites repeatedly bit and fed on the BSF bodily fluids, causing distress. The implications of mite infestation on colony health and viability are discussed, emphasising the need to maintain colony hygiene. Lastly, the apparent metabolisable energy (AME) and standardised ileal digestibility coefficients (SIDC) of amino acids (AA) of full-fat BSFL and BSFP meals for broiler chickens were determined. The AME and SIDC of BSFL and BSFP were higher than those reported for SBM, the commonly used protein meal in poultry diets. The findings demonstrated that BSFL and BSFP meals are better sources of energy and digestible AA, and are potential substitutes for SBM. Although the principles behind BSF bioconversion technology may seem straightforward, effective implementation requires deeper understanding of its complex stages. The present thesis provided a thorough overview of BSF technology, including rearing methods, optimising pupation conditions, the identification of a novel ectoparasite affecting BSF colonies, and the potential use of BSFL and BSFP into broiler chicken diets. By addressing these key aspects, the research contributes valuable insights for optimising BSF production and utilisation, particularly for small and medium-scale operations.Item Genomic architecture of resistance to latania scale (H. lataniae) in kiwifruit (A. chinensis var. chinensis)(BioMed Central Ltd, 2023-10-31) Flay C; Tahir J; Hilario E; Fraser L; Stannard K; Symonds V; Datson PBACKGROUND: Latania scale (Hemiberlesia lataniae Signoret) is an armoured scale insect known to cause damage to kiwifruit plants and fruit, which ultimately reduces crop values and creates post-harvest export and quarantine issues. Resistance to H. lataniae does exist in some commercial cultivars of kiwifruit. However, some of the commercial cultivars bred in New Zealand have not inherited alleles for resistance to H. lataniae carried by their parents. To elucidate the architecture of resistance in the parents and develop molecular markers to assist breeding, these experiments analysed the inheritance of resistance to H. lataniae from families related to commercial cultivars. RESULTS: The first experiment identified a 15.97 Mb genomic region of interest for resistance to H. lataniae in rtGBS data of 3.23 to 19.20 Mb on chromosome 10. A larger population was then QTL mapped, which confirmed the region of interest as the sole locus contributing to H. lataniae resistance. inDel markers mapping the region of low recombination under the QTL peak further narrowed the region associated with H. lataniae resistance to a 5.73 Mb region. CONCLUSIONS: The kiwifruit populations and genomic methods used in this study identify the same non-recombinant region of chromosome 10 which confers resistance of A. chinensis var. chinensis to H. lataniae. The markers developed to target the H. lataniae resistance loci will reduce the amount of costly and time-consuming phenotyping required for breeding H. lataniae scale resistance into new kiwifruit cultivars.Item Plant germplasm diversification strategies : a case study using Limonium : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Plant Science at Massey University, Palmerston North, New Zealand(Massey University, 2024) Cordoba-Sanchez, JuanaLimonium Mill. was chosen for this research as it has an established market for ornamental use and faces significant challenges in breeding including access to germplasm with traits of interest, self-incompatibility in most species, and pollen/stigma dimorphism which limits the types of cross combinations that can be performed. In interspecific crosses, challenges can be the low hybridisation rate (<1%), and the sterility/low fertility of interspecific hybrids. To address these challenges, increase the germplasm diversity available, and speed the development of cultivars, two breeding strategies were evaluated in this research: ploidy manipulation and physically induced mutations. The main outcomes were: 1. Efficacy of those strategies in: • Increasing the ploidy levels of the selected genotypes and therefore the germplasm diversity for The New Zealand Institute for Plant & Food Research Ltd (PFR)’s germplasm bank. • Increasing the hybridisation rate in interspecific crosses. • Fertility restoration in interspecific hybrids 2. Development of plants with new characteristics or different ploidy levels (i.e., triploids, tetraploids, or even higher ploidy levels). 3. Breeding protocols for Limonium using N2O which could be further used in other plant breeding programmes. The use of Limonium for the development of a new breeding strategies for increasing genetic diversity has a direct impact on other breeding programmes i.e., food crops. In addition, the Limonium industry could have access to continued novelty, ensuring industry access to new cultivars would benefit New Zealand’s economy mainly through royalties.Item Mining the 99 Lives Cat Genome Sequencing Consortium database implicates genes and variants for the Ticked locus in domestic cats (Felis catus)(John Wiley and Sons Ltd on behalf of Stichting International Foundation for Animal Genetics, 2021-06) Lyons LA; Buckley RM; Harvey RJ; 99 Lives Cat Genome ConsortiumTabby patterns of fur coats are defining characteristics in wild and domestic felids. Historically, three autosomal alleles at one locus (Tabby): Abyssinian (Ta ; a.k.a. ticked), mackerel (Tm ; a.k.a. striped) and blotched (tb ; a.k.a. classic, blotched) were thought to control these patterns in domestic cats and their breeds. Currently, at least three loci influence cat tabby markings, two of which are designated Tabby and Ticked. The Tabby locus is laeverin (LVRN) and affects the mackerel and blotched patterns. The unidentified gene for the Ticked locus on cat chromosome B1 was suggested to control the presence or absence of the ticked pattern (Tabby - Abyssinian (Ta ; a.k.a. ticked). The cat reference genome (Cinnamon, the Abyssinian) has the ticked phenotype and the variant dataset and coat phenotypes from the 99 Lives Cat Genome Consortium (195 cats) were used to identify candidate genes and variants associated with the Ticked locus. Two strategies were used to find the Ticked allele(s), one considered Cinnamon with the reference allele or heterozygous (Strategy A) and the other considered Cinnamon as having the variant allele or heterozygous (Strategy B). For Strategy A, two variants in Dickkopf Wnt Signaling Pathway Inhibitor 4 (DKK4), a p.Cys63Tyr (B1:41621481, c.188G>A) and a less common p.Ala18Val (B1:42620835, c.53C>T) variant are suggested as two alleles influencing the Ticked phenotype. Bioinformatic and molecular modeling analysis suggests that these changes disrupt a key disulfide bond in the Dkk4 cysteine-rich domain 1 or Dkk4 signal peptide cleavage respectively. All coding variants were excluded as Ticked alleles using Strategy B.Item Werewolf, There Wolf: Variants in Hairless Associated with Hypotrichia and Roaning in the Lykoi Cat Breed.(MDPI (Basel, Switzerland), 2020-06-22) Buckley RM; Gandolfi B; Creighton EK; Pyne CA; Bouhan DM; LeRoy ML; Senter DA; Gobble JR; Abitbol M; Lyons LA; 99 Lives ConsortiumA variety of cat breeds have been developed via novelty selection on aesthetic, dermatological traits, such as coat colors and fur types. A recently developed breed, the lykoi (a.k.a. werewolf cat), was bred from cats with a sparse hair coat with roaning, implying full color and all white hairs. The lykoi phenotype is a form of hypotrichia, presenting as a significant reduction in the average numbers of follicles per hair follicle group as compared to domestic shorthair cats, a mild to severe perifollicular to mural lymphocytic infiltration in 77% of observed hair follicle groups, and the follicles are often miniaturized, dilated, and dysplastic. Whole genome sequencing was conducted on a single lykoi cat that was a cross between two independently ascertained lineages. Comparison to the 99 Lives dataset of 194 non-lykoi cats suggested two variants in the cat homolog for Hairless (HR) (HR lysine demethylase and nuclear receptor corepressor) as candidate causal gene variants. The lykoi cat was a compound heterozygote for two loss of function variants in HR, an exon 3 c.1255_1256dupGT (chrB1:36040783), which should produce a stop codon at amino acid 420 (p.Gln420Serfs*100) and, an exon 18 c.3389insGACA (chrB1:36051555), which should produce a stop codon at amino acid position 1130 (p.Ser1130Argfs*29). Ascertainment of 14 additional cats from founder lineages from Canada, France and different areas of the USA identified four additional loss of function HR variants likely causing the highly similar phenotypic hair coat across the diverse cats. The novel variants in HR for cat hypotrichia can now be established between minor differences in the phenotypic presentations.Item Identification of Genomic Regions Associated with Concentrations of Milk Fat, Protein, Urea and Efficiency of Crude Protein Utilization in Grazing Dairy Cows(MDPI (Basel, Switzerland), 2021-03-23) Ariyarathne HBPC; Correa-Luna M; Blair HT; Garrick DJ; Lopez-Villalobos NAbstract The objective of this study was to identify genomic regions associated with milk fat percentage (FP), crude protein percentage (CPP), urea concentration (MU) and efficiency of crude protein utilization (ECPU: ratio between crude protein yield in milk and dietary crude protein intake) using grazing, mixed-breed, dairy cows in New Zealand. Phenotypes from 634 Holstein Friesian, Jersey or crossbred cows were obtained from two herds at Massey University. A subset of 490 of these cows was genotyped using Bovine Illumina 50K SNP-chips. Two genome-wise association approaches were used, a single-locus model fitted to data from 490 cows and a single-step Bayes C model fitted to data from all 634 cows. The single-locus analysis was performed with the Efficient Mixed-Model Association eXpedited model as implemented in the SVS package. Single nucleotide polymorphisms (SNPs) with genome-wide association p-values ≤ 1.11 × 10−6 were considered as putative quantitative trait loci (QTL). The Bayes C analysis was performed with the JWAS package and 1-Mb genomic windows containing SNPs that explained > 0.37% of the genetic variance were considered as putative QTL. Candidate genes within 100 kb from the identified SNPs in single-locus GWAS or the 1-Mb windows were identified using gene ontology, as implemented in the Ensembl Genome Browser. The genes detected in association with FP (MGST1, DGAT1, CEBPD, SLC52A2, GPAT4, and ACOX3) and CPP (DGAT1, CSN1S1, GOSR2, HERC6, and IGF1R) were identified as candidates. Gene ontology revealed six novel candidate genes (GMDS, E2F7, SIAH1, SLC24A4, LGMN, and ASS1) significantly associated with MU whose functions were in protein catabolism, urea cycle, ion transportation and N excretion. One novel candidate gene was identified in association with ECPU (MAP3K1) that is involved in post-transcriptional modification of proteins. The findings should be validated using a larger population of New Zealand grazing dairy cows.Item The utility of age at puberty and anogenital distance as early-in-life predictors of an animal’s genetic merit for fertility during lactation in New Zealand dairy cattle : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Animal Science, AL Rae Centre of Genetics and Breeding, Massey University, Manawatū, New Zealand(Massey University, 2023) Stephen, Melissa AnneBackground. The New Zealand (NZ) dairy sector is predominantly pasture-based, with low-cost farm systems heavily dependent upon good alignment between the herd’s feed demand and the seasonal supply of pasture. The feed demand of the herd varies across the season according to lactational performance and the physiological status of the cows. Therefore, management of the timing and spread of reproductive events are critical drivers of farm profit. Cows in NZ normally calve annually between July and September each year to ensure that the peak feed demand of the herd coincides with increased spring pasture growth. Adhering to a strictly annual calving interval is biologically challenging for dairy cows, and at least 10% of the national herd is culled each year due to reproductive failure. Selection for fertility provides a long-term tool that can genetically improve the reproductive performance of the national dairy herd. Gains in reproductive performance can contribute to improved pasture utilization, days in milk, cow longevity and, ultimately, farm profitability. Unfortunately, evaluating traits that represent reproductive success during lactation is challenging. The calving, breeding, and pregnancy date phenotypes required for evaluation typically have low heritabilities and are expressed relatively late in an animal’s life, when cows are at least two years of age. Higher heritability traits that exhibit at least moderate genetic correlations with target fertility traits can have value as predictor traits, especially if they are expressed earlier in life than the target trait itself. Two candidate predictor traits for evaluating genetic merit for fertility during lactation are age at puberty (AGEP) and anogenital distance (AGD). Objectives. There were four key objectives of this thesis. First, to investigate a cost-effective approach for measuring AGEP for the purpose of genetic evaluation. Second, to estimate the heritabilities of both AGEP and AGD in NZ Holstein-Friesian cattle, and third to estimate the genetic correlations between fertility during lactation and both AGEP and AGD. Finally, I aimed to undertake a Genome-Wide Association Study (GWAS) to identify genomic regions associated with variation in each of these candidate predictor traits. Materials and Methods. I used data from a study population of 5,010 predominantly Holstein-Friesian and Holstein-Friesian cross Jersey cows, born in 2018 across 54 commercial pasture-based dairy herds. Elevated blood plasma progesterone (BP4) concentrations were used as an indicator of an animal’s puberty status, with animals considered post-pubertal once their BP4 was >1 ng/mL. Each animal was blood tested on three occasions, when the average age of the animals in their herd cohort was around 10, 11 and 12 months of age. These age at first BP4 elevation (AGEP4) phenotypes (n = 4,688) are an example of a censored phenotype, as each animal’s phenotype was only known to fall within a lower or upper bound, rather than being known precisely. Anogenital distance was measured at about 11 months of age (AGD1; n = 4,688) as the distance between the anus and the clitoris using digital calipers. These animals were subsequently followed through first and second lactation, and binary calving (calved in the first 42 d of the seasonal calving period; first n = 4,327; second n = 3,575), breeding (bred within the first 21 d of the seasonal breeding period; first n = 4,111; second n = 3,507) and pregnancy (pregnant within the first 42 d of the seasonal breeding period; first n = 3,939; second n = 3,353) rate traits were recorded. A second measure of AGD was taken when the animals were around 29 months of age (AGD2) in a subset of herds (n=17; 1,956 animals). Results. Overall, variance parameter and breeding value estimation for AGEP4 were remarkably robust to phenotype censoring, and reducing the blood testing regime down to a single BP4 test per animal may be sufficient for the purpose of genetic analysis. I used Markov chain Monte Carlo (MCMC) techniques applying a single site Gibbs sampler to obtain samples from the posterior distributions of (co)variance parameters between AGEP4, AGD and fertility during lactation. The AGEP4 trait had a moderate heritability with a posterior mean of 0.34 and 90% of estimated samples falling within a credibility interval (90% CRI) of 0.30 to 0.37. The heritabilities of AGD were slightly lower at 0.23 (90% CRI 0.20 to 0.26) and 0.29 (90% CRI 0.24 to 0.34) when measured at 11 months and 29 months of age, respectively. Calving, breeding, and pregnancy rate traits exhibited moderate genetic correlations with AGEP4 (0.11 to 0.60), AGD1 (0.19 to 0.52) and AGD2 (0.46 to 0.63). The GWAS analysis of AGEP identified 1 genomic window on chromosome 5 that was associated with variation in AGEP4. Another 4 regions of decreasing importance, located on chromosomes 14, 6, 1 and 11, were identified with suggestive associations with AGEP4. In addition, 2 regions on chromosome 20 and 13 were suggestively associated with variation in AGD1, but there were no associations with AGD2, possibly because this trait was measured in fewer animals. Conclusion. I conclude that both AGEP and AGD are moderately heritable traits, which likely have value as early-in-life genetic predictors for reproductive success during lactation in NZ Holstein-Friesian and Holstein-Friesian cross Jersey cattle.Item Reproductive consequences of genetic improvement in clean fleece production in ultrafine Merino ewes : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Animal Science, Massey University, Palmerston North, New Zealand(Massey University, 2023) Ramos, ZullyTo date, genetic improvement of Uruguayan Merino sheep has focused on selection for reduced fibre diameter (FD) and increased clean fleece weight (CFW) and live weight (LW). The effects of selection for these traits on ewe productive and reproductive performance have not been studied in Uruguay. The aim of this thesis was to evaluate the impact of a long-term selection program applied in an Uruguayan Merino flock between 1999 and 2018. Phenotypic responses of yearling lambs and adult ewes across 20 years of selection demonstrated that selection strategies applied in the flock resulted in heavier animals that produced heavier and finer fleeces. These phenotypic responses were accompanied by a decrease in body condition score (BCS) at mating, with a small positive change in ewe reproductive performance. Strong positive genetic correlations were found between yearling and adult expressions of FD, CFW, and LW. The genetic relationships between FD and reproduction traits were negligible. There were generally favorable genetic correlations between LW and reproduction traits. The genetic relationships between adult CFW and ewe reproductive performance were unfavorable. Genetic trends indicated that the breeding strategies applied during the study period were effective in improving genetic merit in the traits under selection (FD, CFW, and LW) and caused only marginal genetic changes in BCS at mating and ewe reproductive performance. A total of 13, 22, 42, 22, 24 and 29 genomic regions were significantly associated with FD, CFW, LW at mating, BCS at mating, pregnancy rate, and lambing potential, respectively. The results obtained in this thesis will be used to refine the breeding programmes for Merino sheep in Uruguay in the future.