Using an Algorithm to Fit a GAMLSS Model on Dry Matter Data from Brachiaria brizantha.

<b>Background and Objective:</b> Forage production in the tropics is generally asymmetrically distributed. Hence the need to use more complex models, especially when multiple comparisons are made and there are very large deviations from normality. The objective of this research is to fit a Generalized Additive Model for Location, Scale and Shape (GAMLSS) model on accumulated dry matter data from <i>Brachiaria brizantha</i> using a model selection algorithm. <b>Materials and Methods:</b> A Box-Cox Power Exponential (BCPE) distribution was adjusted on the dry matter from <i>Brachiaria brizantha</i> data implementing GAMLSS in R (programming language). The accumulated dry matter data for <i>B. brizantha</i> were obtained from a study carried out on a farm in the state of Portuguesa, Venezuela. The explanatory covariate x was the interval between cuts (21, 28, 35 and 42 days). <b>Results:</b> The dependent variable (dry matter) exhibited both skewness and kurtosis. GAMLSS allowed flexible modeling of both the distribution of the dry matter yield from <i>B. brizantha</i> and the dependence of all the parameters of the distribution on intervals between cuttings. For the dry matter yield from <i>B. brizantha</i>, which exhibited skewness and leptokurtosis, the BCPE distribution, provided the best fit. <b>Conclusion:</b> The interval between cuttings showed an effect that is reflected in the average yield of dry matter from <i>B. brizantha</i>. The interval between cuts affected the skewness and the kurtosis of the distribution.

Effect of Photoperiod with Sunlight at Thermal Stress and Sperm Parameters in Guinea Pigs.

<b>Background and Objective:</b> Photoperiod can regulate reproductive physiological processes in mammals, in which improvements in testosterone concentration, testicular volume and seminal quality have been reported. The aim was to evaluate the influence of photoperiod treatments on guinea pigs' spermatic parameters. <b>Materials and Methods:</b> Thirty guinea pigs, between males and females, were distributed in two rooms with the photoperiodic treatment of 10 hrs light and 14 hrs dark (PT₁ with artificial photoperiod and PT₂ photoperiod with sunlight by opening windows from 08:00-18:00) and one without any direct light stimulus (PT₀) for 78 days. The temperature and humidity were recorded and the TH index was calculated for each room. The sperms were recovered in Tris base medium from the epididymis of 16 males to determine sperm concentration, motility, kinetic parameters, vitality, HOST, acrosomal integrity and DNA fragmentation. <b>Results:</b> Sperm values in PT₁ and PT₀ were similar but PT₂ obtained values lower in sperm concentration, non-progressive motility, total motility, VCL, ALH, vitality, HOST+, acrosomal integrity, sperm with non-fragmented DNA and no pregnancies were reported (0/5). A 100% pregnancy was observed in PT₀ (4/4) and 50% in PT₁ (2/4). However, precocity was evidenced in PT₁ compared to PT₀. PT₂ recorded higher peaks in temperature (33.8°C, THI 81, considered as thermal stress) compared to PT₀ (32.65°C, THI 81.8) and PT₁ (32.75°C, THI 81.6). <b>Conclusion:</b> An artificial photoperiod can improve sperm characteristics and reproductive precociousness of guinea pigs, unlike the photoperiod with sunlight, which generated low spermiogram values and absence of pregnancy due to thermal stress.