Animals Of High Genetic Merit Research Articles

Emerging Contributions of Pluripotent Stem Cells to Reproductive Technologies in Veterinary Medicine.

The generation of mature gametes and competent embryos in vitro from pluripotent stem cells has been successfully achieved in a few species, mainly in mice, with recent advances in humans and scarce preliminary reports in other domestic species. These biotechnologies are very attractive as they facilitate the understanding of developmental mechanisms and stages that are generally inaccessible during early embryogenesis, thus enabling advanced reproductive technologies and contributing to the generation of animals of high genetic merit in a short period. Studies on the production of in vitro embryos in pigs and cattle are currently used as study models for humans since they present more similar characteristics when compared to rodents in both the initial embryo development and adult life. This review discusses the most relevant biotechnologies used in veterinary medicine, focusing on the generation of germ-cell-like cells in vitro through the acquisition of totipotent status and the production of embryos in vitro from pluripotent stem cells, thus highlighting the main uses of pluripotent stem cells in livestock species and reproductive medicine.

A refined culture system of oocytes from early antral follicles promotes oocyte maturation and embryo development in cattle.

The proposed culture system improves the current state of in vitro culture of growing oocytes in the bovine species and allows access to the untapped gamete reserve, thus improving reproductive efficiency. The present study aimed to improve the in vitro culture of bovine oocytes collected from early antral follicles (EAFs) to support the progressive acquisition of meiotic and developmental competence. The rationale that drove the development of such a culture system was to maintain as much as possible the physiological conditions that support the oocyte growth and differentiation in vivo. To this extent, oocytes were cultured for 5 days, which parallels the transition from early to medium antral follicles (MAFs) in the bovine, and supports promoting a 3D-like structure were provided. Additionally, the main hormones (follicle-stimulating hormone, estradiol, progesterone, and testosterone) were added in concentrations similar to the ones previously observed in bovine EAFs. The meiotic arrest was imposed using cilostamide. The cultured cumulus-oocyte complexes (COCs) reached a mean diameter of 113.4 ± 0.75 µm and showed a progressive condensation of the chromatin enclosed in the germinal vesicle (GV), together with a gradual decrease in the global transcriptional activity, measured by 5-ethynyl uridine incorporation. The described morpho-functional changes were accompanied by an increased ability to mature and develop to the blastocyst stage in vitro, although not matching the rates obtained by MAF-retrieved oocytes. The described system improves the current state of in vitro culture of growing oocytes in the bovine species, and it can be used to increase the number of gametes usable for in vitro embryo production in animals of high genetic merit or with specific desirable traits.

The impact of genetic merit on ewe performance and efficiency parameters.

The aim of this study was to investigate the impact of ewe genetic merit on ewe performance and efficiency parameters. The study consisted of three genetic merit groups (New Zealand [NZ], High Irish, and Low Irish) and ran from 2016 to 2019, inclusive. Each genetic merit group contained 30 purebred Suffolk and 30 purebred Texel ewes, which were selected based on their maternal genetic indexes in their country of origin, namely Ireland (€uro-star Replacement index) or New Zealand (New Zealand Maternal worth). Ewe body condition score (BCS), ewe body weight (BW), milk yield, milk composition, dry matter intake (DMI), and efficiency parameters were all analyzed using linear mixed models. Ewe BW was similar across all genetic merit groups at each time point (P > 0.05). In comparison to both High and Low Irish ewes, NZ ewes had a higher BCS at mating, mid-pregnancy, lambing, week 10 post-lambing (PL, P < 0.05). Ewe BW change was similar across genetic merit groups, except between mating and mid-pregnancy where ewe BW loss was greater for NZ ewes than Irish ewes (P < 0.05) and between weeks 6 PL and 10 PL, where NZ ewes gained BW and High and Low Irish ewes lost BW (P < 0.01). Ewe milk yield, milk fat, total solids, and gross energy content were superior for milk produced by NZ ewes at week 6 PL in comparison to milk produced by High Irish and Low Irish ewes (P < 0.01). NZ ewes produced a greater quantity of milk solids/kg of BW at week 6 PL compared with High Irish ewes (P < 0.01), whereas Low Irish ewes did not differ from either NZ or High Irish (P > 0.05). Low Irish ewes had a greater daily DMI than High Irish ewes in late lactation (week 10 PL, P < 0.05) and had a greater DMI/kg of ewe BW compared with the High Irish ewes at the same time point (P < 0.05). NZ ewes weaned a litter BW equivalent to 60.4% of their mating BW, which was more than the Low Irish ewes who weaned 57.1% of the ewe’s BW at mating (P < 0.01), whereas the High Irish ewes did not differ from either the NZ or Low Irish ewes at 59.3% of the ewe’s BW at mating (P > 0.05). This study presents a range of parameters across ewes of high and low genetic merit, demonstrating the ability to achieve gains through selection of animals of high genetic merit. Sheep producers should consider genetic indexes as a tool to assist in the decision-making process of selecting replacement ewes and/or breeding rams, once satisfied the animal is correct, and meeting the breeding objectives of the system.

A comparison of farm labour, profitability, and carbon footprint of different management strategies in Northern European grassland sheep systems

CONTEXTSheep production systems need to become more carbon efficient to meet growing public demands on climate change. Some of the ways postulated to achieve this is to implement new technologies and management strategies such as precision livestock farming (PLF), increased use of high genetic merit animals with estimated breeding values through artificial insemination (AI) where practical, and the use of prolific breeds. However, the carbon footprint impact of these strategies has not to-date been quantified. Additionally, international experience indicates that uptake of such strategies is low due, in part, to the perception of increased workload especially during busy periods of the sheep year. OBJECTIVESThis trans-European study investigates the impact of differing sheep management strategies on farm labour input, carbon footprint as well as the on-farm profitability, to address these concerns. METHODSFour management strategies were considered i) use of technology (PLF), ii) use of performance recording for higher genetic merit, iii) use of AI for higher genetic merit and iv) and use of prolific breeds, in 14 case study flocks located in areas typical of Northern European grassland sheep production systems across Scotland, France, Ireland and Norway. For each management strategy, paired case study flocks were identified. Labour was assessed at key handling events using video recording, farmers' diaries, and questionnaires, which were later quantified and classed into key tasks to create normalised labour profiles for each case study flock. The carbon footprint was quantified using a carbon calculator tool (www.agrecalc.com). Financial net margins were calculated. RESULTS AND CONCLUSIONSResults highlighted that introducing PLF technology on extensive farms reduced labour by 20% and increased economic margins by £9/ewe but with a concurrent increase in carbon emissions (kg CO2e/ kg of meat produced). Using performance recording on sheep farms for achieving higher genetic merit increased economic margins by £6/ewe, and reduced carbon emissions (kg CO2e) per kg of meat produced but resulted in 10% extra labour. AI on farms increased economic margins by £50/ewe, did not incur extra labour and increased carbon efficiency in terms of kg CO2e/kg meat produced. Finally, high prolific breeds did not significantly increase labour input at key handling events and resulted by higher economic margins (+£3/ewe), without a change in terms of kg CO2e/kg meat produced. SIGNIFICANCEThese novel case studies clearly illustrate it is possible to increase carbon and labour efficiency by adopting technology, changing breeding management or ewe breed on sheep farms.

A new Approach for Accurate Detection of Chromosome Rearrangements That Affect Fertility in Cattle.

Simple SummaryGlobally, cattle production has more than doubled since the 1960s, with widespread use of artificial insemination (AI) and an emphasis on a small pool of high-genetic-merit animals. Selecting AI bulls with optimal fertility is therefore vital, as impaired fertility reduces genetic gains and reduces production, resulting in heavy financial and environmental losses. Chromosome translocations, where large parts of the genome are inappropriately attached in abnormal patterns, are a common cause of reduced fertility; however, reciprocal translocations are significantly underreported due to the difficulties inherent in analysing cattle chromosomes. Based on our previous work, we have developed an approach for the unambiguous detection of abnormalities that affect fertility. We applied this method on the chromosomes of 39 bulls, detecting multiple abnormalities that affect fertility, including those that would be undetectable using traditional screening techniques. With UK dairy calving rates of only 50–60%, it is vital to reduce further fertility loss in order to maximise productivity. The approach developed here identifies abnormalities that DNA sequencing will not, and has the potential to lead to long-term gains, delivering meat and milk products in a more cost-effective and environmentally-responsible manner to a growing population.Globally, cattle production has more than doubled since the 1960s, with widespread use of artificial insemination (AI) and an emphasis on a small pool of high genetic merit animals. Selecting AI bulls with optimal fertility is, therefore, vital, as impaired fertility reduces genetic gains and production, resulting in heavy financial and environmental losses. Chromosome translocations, particularly the 1;29 Robertsonian translocation, are a common cause of reduced fertility; however, reciprocal translocations are significantly underreported due to the difficulties inherent in analysing cattle chromosomes. Based on our porcine work, we have developed an approach for the unambiguous detection of Robertsonian and reciprocal translocations, using a multiple-hybridization probe detection strategy. We applied this method on the chromosomes of 39 bulls, detecting heterozygous and homozygous 1;29 translocations and a 12;23 reciprocal translocation in a total of seven animals. Previously, karyotype analysis was the only method of diagnosing chromosomal rearrangements in cattle, and was time-consuming and error-prone. With calving rates of only 50–60%, it is vital to reduce further fertility loss in order to maximise productivity. The approach developed here identifies abnormalities that DNA sequencing will not, and has the potential to lead to long-term gains, delivering meat and milk products in a more cost-effective and environmentally-responsible manner to a growing population.

10 Pregnancy rates following artificial insemination or embryo transfer in lactating Holstein cows

Excessive heat affects the fertility of high production lactating cows, and reduced pregnancy rates (PR) are observed during summer and early fall. Embryo production programs are used to produce more calves from high genetic merit animals, but could it also increase fertility by bypassing all the negative variables affecting the embryo development before Day 7 (oocyte development, ovulation, fertilization, early embryo development)? The data from AIs and embryo transfers (ET) between June 2017 and May 2019 were analysed. June, July, August, September, and October were called critical months (first-service AI conception rate dropped below 44%). The cows were located at Maddox Dairy in Riverdale, CA, USA, a Holstein herd that milks 3500 cows with a 305-day mature-equivalent milk production of 12 800 kg. First- and second-lactation cows were enrolled in a Presynch-Ovsynch oestrus-synchronization program and scheduled for the first AI at 86 days after calving or to receive an embryo 7 or 8 days after the expected heat. The embryos were produced invivo or invitro from Holstein donors and were transferred fresh or frozen. Blood was sampled on Day 30 after expected heat day (23 days after embryo transfer), and pregnancy was detected by the IDEXX PAG Bovine Pregnancy Test. Table 1 summarises the results, where ET PR% is the number of pregnant cows divided by the number of cows that received and embryo. All the cows synchronized for AI were bred, but only cows with the presence of a corpus luteum (CL) on ET day received an embryo. The presence of a CL was not detected in 28.7% (471/1642) of the cows (32.2% in the critical months and 25.7% in the others). Unfortunately, we could not detect the presence of a CL by ultrasonography every time we transferred embryos, so the nonovulation rate might be overestimated. The cows without a CL were considered open and used to calculate the adjusted PR (AdjPR%). Embryo transfer PR is superior to that of AI, especially during the critical months. Fresh invivo embryos have the most impact. When the cows without CLs are considered open, the difference between AI and ET is still evident for fresh invivo embryos. Besides producing animals with higher genetic merit, depending on the type of embryo used, ET can increase fertility in lactating Holstein cows, especially during the critical months. The other benefit of using ET is that cows that do not ovulate are synchronized right away, which is not the case for AI cows. Table 1.AI×embryo transfer in lactating Holstein cows1 from June 2017 to May 20192 Item Critical months (June to October) Other months (November to May) All year %PR n Adj PR% n %PR n Adj PR% n %PR n Adj PR% n Artificial insemination 41.2% 896 41.2% 896 47.7% 1767 47.7% 1767 45.5% 2663 2663 Fresh invivo embryo 62.7% 373 47.5% 493 69.5% 262 55.3% 329 65.5% 635 50.6% 822 Frozen invivo embryo 59.3% 221 44.8% 292 59.4% 256 47.3% 322 59.3% 477 46.1% 614 IVF fresh embryo 47.9% 167 36.2% 221 54.0% 363 43.0% 456 52.1% 530 40.8% 677 Total embryos 58.5% 761 44.2% 1006 60.2% 881 47.9% 1107 59.4% 1642 46.1% 2113 1Lactating Holstein cows, first and second lactation, first service, Presynch-Ovsynch, 85 DIM. 2PR%=the number of pregnant cows divided by the number of cows that received and embryo; AdjPR%=adjusted pregnancy rate.

Genetic market in cattle (Bull, AI, FTAI, MOET and IVP): financial payback based on reproductive efficiency in beef and dairy herds in Brazil.

A number of reproductive biotechnologies are currently available to multiply offspring from high genetic merit animals to enhance reproductive efficiency and profitability both in dairy and beef herds. Some of these technologies such as fixed time artificial insemination (FTAI), when correctly implemented, generally allow greater reproductive performance than natural breeding. Besides the use of frozen-thawed semen during artificial insemination, cattle recipients can also be synchronized to receive embryos (produced in vivo or in vitro) at set dates with fertility results that usually outperforms natural breeding as well as artificial insemination (AI), particularly during warm seasons and in repeat breeders cows. Altogether, the use of hormonal programs to synchronize ovulation time simplify field routine, can easily fix physiological limitations related to postpartum anestrus (beef cows), poor estrus detection efficiency due to less evident estrus signs (dairy cows), making AI and ET viable to commercial herds both in terms of results and economical returns.

Evaluación Genética de un Plantel de Cuyes Reproductores de Genotipo Perú

El presente estudio tuvo por objetivo la evaluación genética de parte de los animales del plantel de cuyes reproductores de genotipo Perú pertenecientes a la Estación Experimental Agraria Canaán del Instituto Nacional de Innovación Agraria de Ayacucho, Perú, para características de peso vivo al beneficio (PB) y velocidad de crecimiento (VC). Se empleó la información productiva y de parentesco de 162 cuyes, además del sexo, tipo de parto, mes de nacimiento y peso de la madre al parto, cuyo análisis de incidencia sobre las variables estudiadas se efectuó mediante un modelo de efectos fijos. La estimación de los valores de cría se realizó a través de un modelo animal-BLUP unicarácter, el cual incluyó como efectos fijos a aquellos factores ambientales sistemáticos de incidencia significativa, además de los efectos aleatorios derivados de los factores genéticos de los animales. Los componentes de (co)varianza incluidos en el modelo y los algoritmos computacionales fueron resueltos usando el software VCE4 v. 4.2 y PEST v. 4.0, respectivamente. Los valores de cría estimados para PB y VC alcanzaron desvíos de -84.56 a 79.28 g y de 1.39 a -1.26 g/día, mientras que sus niveles de precisión variaron de 28.81 a 89.37% y 28.46 a 88.35%, respectivamente. La alta dispersión de los valores de crías y la elevada correlación genética entre los caracteres evaluados, permitió identificar animales con un alto mérito genético, ameritando su uso potencial como padres de la siguiente generación.

Amino acid profiles in first trimester amniotic fluids of healthy bovine cloned pregnancies are similar to those of IVF pregnancies, but not nonviable cloned pregnancies

Somatic cell nuclear transfer (SCNT), or cloning, is one of the assisted reproductive technologies currently used in agriculture. Commercial applications of SCNT are presently limited to the production of animals of high genetic merit or the production of the most elite show cattle owing to its relatively low efficiency. In current practice, 20% to 40% of SCNT pregnancies do not result in viable offspring. In an effort to better understand some of the anomalies associated with SCNT pregnancies, we investigated amino acid compositions of first trimester amniotic fluid. In this retrospective study, amniotic fluids were collected from SCNT and control IVF pregnancies at Day 75 of gestation and grouped according to the pregnancy results: control IVF (IVF), viable SCNT pregnancies that resulted in live healthy calves (SCNT-HL), nonviable SCNT pregnancies that were aborted before Day 150 (SCNT-ED), and nonviable SCNT pregnancies that were aborted after Day 150 or produced deceased calves (SCNT-LD). High-performance liquid chromatography (HPLC) was used to analyze the concentrations of 22 amino acids (AAs) in the amniotic fluid samples. There were no differences in average AA concentrations between IVF and SCNT-HL groups, whereas SCNT-LD and SCNT-ED had higher levels of total AA concentrations. Concentrations of asparagine, citruline, arginine, and valine were significantly higher in the SCNT-LD group. Both SCNT-LD and SCNT-ED groups had relatively large intragroup variances in AA concentrations. Urea concentration was also measured in the SCNT amniotic fluid samples. No correlations between urea concentrations and arginine concentrations or pregnancy outcomes were found. The findings in this study not only deepen the understanding on SCNT pregnancy anomalies, but also provide a potentially useful screening tool for assessing viable and nonviable SCNT pregnancies.

Genómica en la producción animal

El mejoramiento genético evalúa y utiliza la variación genética para mantener y mejorar cualitativa y cuantitativamente la producción animal. La identificación de animales con altos méritos genéticos se dificulta por el hecho que la mayoría de las características de importancia económica, por ser de naturaleza cuantitativa, son controladas por varios genes los cuales interactúan con el medio ambiente. El objetivo de este documento fue realizar una revisión sobre la aplicación de la genómica en la producción animal para diferentes características tanto las asociadas a la producción de leche como carne y la disponibilidad actual de herramientas de genética molecular y genómica que permiten predecir con mayor precisión los valores genéticos de los animales desde su nacimiento, disminuyendo el intervalo entre generaciones y aumentando la intensidad de selección.

What ‘animal models’ can and cannot tell ornithologists about the genetics of wild populations

Good estimates of the genetic parameters of natural populations, such as heritability, are essential for both understanding how genetic variation is maintained and estimating a population’s evolutionary potential. Long-term studies on birds are especially amenable for calculating such estimates because of the ease with which pedigrees can be inferred. Recent ‘animal model’ methodology, originally developed by animal breeders to identify animals of high genetic merit, has been applied to natural bird populations of known pedigree. Animal models are more powerful than traditional analyses such as parent–offspring regression because they use all of the available pedigree information simultaneously. In doing so, they can accommodate common phenomena like selection and inbreeding and are especially suitable for the complex and incomplete pedigrees typical of natural populations. Animal models not only provide a better way of estimating genetic and environmental variance components, they also allow individual phenotypes to be separated into their genetic and environmental components. Here we aim to provide the interested ornithologist with an accessible entry into the vast and sometimes daunting quantitative genetics literature and, in particular, into the literature on the animal model. We outline not only the possibilities offered by the animal model for the accurate estimation of genetic parameters in the wild but also associated potential pitfalls and limitations. On the whole, we aim to provide an accessible and up-to-date overview of the rapidly developing and exciting field of evolutionary genetics applied to long-term studies of wild bird populations.

Reproductive function in average and high yielding dairy cows

AbstractThe resumption of reproductive activity in the early post partum period and the subsequent fertility of dairy cows are of considerable practical and economic importance to the producer. Regular milk progesterone analysis was used in this study to monitor the re-establishment of reproductive cyclicity in animals of average (AGM, n=20) and high genetic merit (HGM, n=28) kept under standard management conditions. The profiles obtained were then characterised into normal and four different types of abnormal activity. Resumption of cycles occurred significantly later in the higher yielding cows than in those of average genetic merit (23 ±2.3 days in HGM cows and 15 ± 1.6 days in AGM cows; P=0.0089). There was a significant increase in the amount of abnormal cycles encountered in the high genetic merit animals compared with average yielding animals (61% and 30% respectively; χ2 test, P=0.045); in particular, the delayed occurrence of ovulation post partum (11% vs 0%) and an increased incidence of persistent corpora lutea (32% vs 20%). For high genetic merit animals, the incidence of abnormal cycles was associated with increased peak milkyields (abnormal cycles: peak milk yield 54.7 ± 1.11 kg/day; normal cycles: peak milk yield 46.4 ± 1.35 kg/day, P=0.002). This relationship was not apparent in average genetic merit animals. First service conception rates were 50% (9/18) for AGM cows and 38% (10/26) for HGM cows (χ2 test, n.s.). The calving to conception interval was 98 ± 9.7 days for AGM animals (n=l7) and 105 ± 9.1 days for HGMs (n=24) (t-test, n.s.). In conclusion, this study confirms that high genetic merit dairy cows have compromised reproductive function in terms of a delayed resumption of cyclicity and an increased incidence of abnormal progesterone cycles, which was associated with higher peak milk yields. There was also a reduced first service conception rate in high yielders although the difference was not significant with this group size.

Genotype with nutrition interaction for protein and lipid deposition in pigs

Testing different pig genotypes on a single diet may constrain protein and lipid deposition or reduce the efficiency of nutrient utilisation by under- or over-supply of nutrients. If the ranking of genotypes is dependent on the diet used when performance testing animals, then genotype-specific nutritional regimes may be required by breeding companies to identify animals of high genetic merit and by producers to realise the benefits obtained by genetic improvement programmes. In the Edinburgh lean growth project, divergently selected lines for efficiency of lean growth (LFC), for rate of lean growth with animals performance tested on ad-libitum (LGA) or restricted (LGS) feeding or for daily food intake (DFI) have been established with seven generations of selection in a Large White population (Cameron, 1994). The selection lines provide an experimental resource to estimate the genotype with nutrition interaction for protein and lipid deposition rates as differences between selection lines will relate to the selection strategy since the lines were derived from the one base population.

A comparison of four contrasting milk production systems for high genetic merit winter calving dairy cows in a grassland based production environment

Meeting the greater nutrient requirements of high genetic merit dairy cows in grassland based systems provides a very real challenge. This study examines the performance of high genetic merit animals, managed on four contrasting grassland based systems of milk production, including both the winter and summer periods.

Options to reduce vulnerability to metabolic stress by genetic selection

AbstractGenetic selection for milk production has been very successful. However to achieve high yields, the metabolic load on dairy cows is believed to be substantial. If the size of this load is large enough then the animal may become ‘metabolically stressed’. Signs of this may include some sort of distortion of normal physiological function. There is evidence from both population studies and research herds to suggest that intense selection for milk yield has led to a deterioration in some aspects of health and fertility. Genetic correlation estimates between production and measures of fertility are unfavourable. As an example, calving intervals of high merit animals from Langhill are on average 12 days longer than those of average genetic merit, which is mostly due to a delay in days to first heat. It is suggested that some aspects of health and fertility problems in high genetic merit animals are a consequence, in part, of so-called metabolic stress. Future breeding goals should be broadened to include a broad spectrum of traits related to efficient milk production, in addition to either health and fertility traits themselves, or traits believed to be precursors of them, such as those related to metabolic stress. The complexity and subjectivity of metabolic stress and its components makes it very difficult to include in future breeding goals. However, traits related to energy balance, such as some measures of condition score, dry-matter intake and live weight may be useful in breeding programmes where one of the goals is to alleviate metabolic stress.

Effect of genetic merit on postpartum follicular development, milk production, body weight and, insulin and glucose levels in dairy cows

Efficient milk production in Ireland in both spring and autumn calving herds is very much dependent on compact calving. This requires an early resumption of ovarian activity, high submission rate, and pregnancy rate to service. Since 1984 there has been an increase in the genetic merit of Irish dairy herds. High genetic merit animals have reduced reproductive performance due to the demands of high milk yield (Nebel and McGilliard, 1993) and the loss of body weight and body condition (Butler and Smith, 1989). However, little comparative data on the reproductive performance of dairy cows of different genetic merit are available. The objective of this study was therefore, to determine the relationship between genetic merit of dairy cows and follicular growth patterns, milk production, body weight loss, insulin and glucose levels in early lactation.

Effect of genetic merit on postpartum follicular development, milk production, body weight and, insulin and glucose levels in dairy cows

Efficient milk production in Ireland in both spring and autumn calving herds is very much dependent on compact calving. This requires an early resumption of ovarian activity, high submission rate, and pregnancy rate to service. Since 1984 there has been an increase in the genetic merit of Irish dairy herds. High genetic merit animals have reduced reproductive performance due to the demands of high milk yield (Nebel and McGilliard, 1993) and the loss of body weight and body condition (Butler and Smith, 1989). However, little comparative data on the reproductive performance of dairy cows of different genetic merit are available. The objective of this study was therefore, to determine the relationship between genetic merit of dairy cows and follicular growth patterns, milk production, body weight loss, insulin and glucose levels in early lactation.

Genotype by diet interactions for liveweight and condition score during lactation in heifers

An earlier study at Langhill (Veerkamp et al, 1995) showed that selection for yield in dairy cows increases body tissue mobilisation during lactation, since high genetic merit animals had a lower average condition score (CS) compared with low genetic merit animals. However, in this study no diet effect for condition score and no interaction between diet and genetic merit was found. The reasons for this might have been that average condition scores during lactation were analysed, and therefore the objective of this study was to evaluate the effects of genotype and diet during lactation using weekly observations.

Preferential choice of diets differing in protein content by pigs divergently selected for lean growth rate

Performance testing several genotypes on one diet may impose nutritional constraints on the genetic merit for growth of particular genotypes. Use of the diet choice procedure may remove nutritional constraints on growth, if pigs can “choose” the appropriate combination of the diets to attain the growth determined by the animal's genotype. In a genetic improvement framework, the diet choice procedure could be used to identify animals of high genetic merit for a given selection objective.There were 120 Large White pigs from the high, low and control lines, which had been selected for lean growth rate for seven generations in the Edinburgh lean growth selection experiment. In each selection line, there were 10 full-sib groups of four pigs. Pigs were performance tested from 30 to 85 kg, with individual penning and ad-libitum feeding. Within each full-sib group, one pig was allocated to each of the high (HP : 220 g crude protein (CP)/kg) or low (LP : 120 g CP/kg) protein diets.

Preferential choice of diets differing in protein content by pigs divergently selected for lean growth rate

Performance testing several genotypes on one diet may impose nutritional constraints on the genetic merit for growth of particular genotypes. Use of the diet choice procedure may remove nutritional constraints on growth, if pigs can “choose” the appropriate combination of the diets to attain the growth determined by the animal's genotype. In a genetic improvement framework, the diet choice procedure could be used to identify animals of high genetic merit for a given selection objective.There were 120 Large White pigs from the high, low and control lines, which had been selected for lean growth rate for seven generations in the Edinburgh lean growth selection experiment. In each selection line, there were 10 full-sib groups of four pigs. Pigs were performance tested from 30 to 85 kg, with individual penning and ad-libitum feeding. Within each full-sib group, one pig was allocated to each of the high (HP : 220 g crude protein (CP)/kg) or low (LP : 120 g CP/kg) protein diets.