Importancia del estatus corporal y de la gestión de las reservas en cerdas hiperprolíficas y su repercusión sobre los índices reproductivos y productivos en condiciones comerciales

Abstract

In the last decades, pig genetic lines with higher productivity capacity and different morphological conditions have been developed, so it is essential to explore in depth the relationship between the morphological and physiological characteristics of the sow and the productive performance. The main OBJECTIVE of this Doctoral Thesis was to deepen the knowledge of the management of body reserves (live weight, backfat thickness, and loin muscle depth) in current hyperprolific sows, fed with commercial diets for the growth, gestation and lactation phases, and their effect on productivity and reproductive performance. In order to achieve the main objective, three specific objectives were set: 1) To evaluate the effect of body weight at first service (gilts) on body reserves (backfat thickness and loin muscle depth) and the productive performance of the sow in her first and subsequent cycles. Objective developed in Chapter 1. 2) To evaluate the effect of different levels of restricted feeding during early gestation (from day 3 to day 28 of gestation) on body reserves, productive and reproductive performance, and hormonal-metabolic status of primiparous and multiparous sows. Objective developed in Chapter 2. 3) Deepen the understanding of the management of body reserves (backfat thickness and loin muscle depth) throughout a complete cycle (gestation, lactation, and post-weaning estrus interval) with commercial gestation and lactation diets in both gilts and non-gilts sows. Objective developed in Chapter 3. Regarding the METHODOLOGY, this Doctoral Thesis focused on applied research under commercial production conditions. For the development of Chapter 1, 360 gilts sows were classified into three groups according to their body weight at first mating (<135 kg; 135-150 kg and >150 kg). The sows were evaluated from the first insemination to the first weaning on parameters related to body reserves, productivity, and hormones related to metabolism. Subsequently, their performances were monitored until they were removed from the herd. To achieve the objectives described in Chapter 2, a total of 130 sows (61 primiparous and 69 multiparous) (based on body weight, backfat thickness, and loin muscle depth) were assigned to one of three experimental groups, where feeding levels from day 3 to day 28 of gestation were 2.50 kg/d, 3.25 kg/d, or 3.75 kg/d. Sows in all groups received the same commercial diet (2.18 Mcal NE kg-1 and 13.72 g CP kg-1). The evolution of body reserves, productive and reproductive parameters, as well as the serum level of hormones related to metabolism, were studied. Finally, for the development of Chapter 3, a total of 283 sows, from 1 to 6 farrowings (mean ± SD; 2.91 ± 1.78), had their backfat and loin muscle thickness recorded on the day of insemination, day 40 and 110 of gestation, and at weaning. Subsequently, the fat/lean tissue ratio was calculated and sows were categorized into 3 levels based on the 25th and 75th percentiles (Low, Medium, and High Groups). All analyses were performed with the statistical software SPSS version 28.0 for Windows (SPSS Inc., Chicago, IL, USA). First, descriptive analyses of the treatment groups were performed, and the normality of the study variables was assessed. Variables with normally distributed data were subjected to parametric analysis by analysis of variance (using models with fixed effects and, in some cases, random effects). However, non-normally distributed variables were analysed by non-parametric analysis (Chi-square test or Kruskal-Wallis test). In addition, Pearson's coefficient was calculated to assess the relationships between body condition and backfat thickness and loin muscle depth. The sow (or her litter, depending on the variable analysed) was considered as the experimental unit. Significance was set at p ≤ 0.05, while 0.05 < p ≤ 0.10 was considered a trend. The main CONCLUSIONS drawn from the conditions of the conducted research are as follows: 1. Sow body weight at first service had a greater effect than age on production parameters in the first and subsequent sow cycles. In addition, it was crucial for improving productive performance at first mating and throughout her life, serving as an early indicator of subsequent productive success. Therefore, on a commercial farm, one of the objectives will be to avoid inseminating sows weighing less than 135 kg, 2. Increasing the level of feeding by up to 50% during the first month of gestation showed no clear benefit in terms of productive or reproductive performance, except for an increase in sow body reserves throughout gestation and at weaning, 3. Periodic measurements of fat and lean tissue proved to be a practical tool to assess the adequacy of feeding programmes on each farm. The fat/lean tissue ratio can provide an objective measure of the nutritional status of sows, allowing optimal management of reserves and reducing the mobilization of lean tissue at the end of gestation and/or lactation, 4. The body reserves differed between gilts and non-gilts sows, with gilts showing lower fat deposition and higher mobilization of lean tissue during gestation and lactation. This fact would justify differentiated feeding programs for both groups of sows,