Given below are two statements: one is labelled as Assertion (A)... | Agrigyan

In cattle, especially in primiparous heifers, feto-maternal disproportion (fetal oversize relative to maternal pelvic area) accounts for roughly 45% to 50% of all dystocia cases, making it by far the most prevalent single cause, followed by abnormal fetal presentation, position, or posture.

Placental classification by chorionic villi distribution:
Cotyledonary placenta (discrete localized tufts of chorionic villi called cotyledons attaching to uterine caruncles forming placentomes) -> Ruminants (Cattle, Sheep, Goat, Buffalo)
Diffuse placenta -> Horse and Pig
Zonary placenta -> Carnivores (Dog and Cat)
Discoid placenta -> Primates and Rodents.

The Doppler equation is $\Delta f = \frac{2 f_0 v \cos \theta}{c}$, where $\theta$ is the insonation angle between the ultrasound beam and the direction of blood flow. When the transducer is oriented parallel to blood flow, $\theta = 0^\circ$ or $180^\circ$, and $|\cos \theta| = 1$ (maximum possible value), yielding the greatest Doppler frequency shift and highest velocity measurement accuracy without angle correction errors. Thus, both (A) and (R) are correct, and (R) explains (A).